diff --git a/CHANGELOG.md b/CHANGELOG.md
index 6878e91..c225d18 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,12 @@ The application version is maintained in `package.json` and displayed in the adm
 
 No changes recorded yet.
 
+## 1.26.0 - 2026-09-30
+
+### Added
+
+- Warm-up / transponder check on Race Day before a heat starts: "Start warm-up" (1, 2 or 3 minutes, with a countdown and voice announcements) lists every driver in the heat, and each one gets a green tick once their transponder crosses the line. A missing driver's transponder can be changed right in the panel, or linked to one of the unknown transponders that just crossed. Start warns about anyone not seen, but can still start the heat. The preflight list shows "Transponder check: 3/4".
+
 ## 1.25.0 - 2026-09-27
 
 ### Added
diff --git a/ROADMAP.md b/ROADMAP.md
index 71b9ab4..fc41b29 100644
--- a/ROADMAP.md
+++ b/ROADMAP.md
@@ -561,6 +561,18 @@ Investigated alongside this, per the user's follow-up question about whether the
 
 Verified 2026-09-12: `npm run test:browser` passes all 37 scenarios (3 new, 34 pre-existing) including the new Guide tabs coverage; `npm test` passes all 205 unit tests unchanged. Live headless-browser checks in both languages confirmed correct tab labels/translations, no raw `guide.*` keys, and that the "Run a race" tab's content (`guide.race_day_title`) renders correctly. Refreshed `docs/screenshots/guide.jpg` to show the new tab bar.
 
+## Warm-up / transponder check before a heat
+
+Asked by the user 2026-09-30: what happens if a driver in a running heat registered the wrong transponder? Checked first: fixing the transponder on the driver mid-heat works for every passing *after* the fix (drivers are looked up per passing), but laps already driven are stuck on an "Unknown driver" row, credited to the wrong driver, or - if the number belonged to someone not in the heat - thrown away entirely with no way to recover them. The user pointed at how other timing systems prevent this instead: a 1-2 minute warm-up where every driver in the heat must show a valid passing (green tick) before the start, with a quick transponder fix for anyone who doesn't. Built that; the mid-heat "move laps" safety net was offered too, and deferred by the user.
+
+- [x] `src/warmup_logic.js` (new, pure): remembers each transponder the main decoder sees (bounded, in memory only - never saved or counted as laps), and builds the per-heat check: which entrants have crossed since the warm-up started, which unknown transponders crossed (naming the owner if it's a driver outside this heat), countdown.
+- [x] `decoder_runtime.js` reports every main-line transponder *before* its running-session check - previously every passing before the start was discarded as `no_running_session`, so nothing could be checked pre-heat.
+- [x] Race Day panel (`race_day_view.js`), shown for a selected, not-yet-started race-format heat with driver transponders (not practice, team race or sponsor/track events): Start warm-up (1/2/3 min) with a live countdown and new voice events `warmup_start` / `warmup_1_minute` / `warmup_end` (sv + en in the sound pack, so Piper pre-generation includes them); ✅/⏳ per driver in start order; for a missing driver, "Link unknown transponder" (one pick) or type a new one - saved on the driver immediately, with the same cross-person conflict warning as the Drivers page. The page refreshes on each passing but never while the operator is typing in a field.
+- [x] Start warns - never blocks, a driver may simply not show up - listing who wasn't seen, and ends the warm-up. Preflight shows "Transponder check: seen/total" as a warning while someone is missing.
+- [x] `tests/browser_fake_decoder.js` can now send real PASSING frames (`sendPassing`), so browser tests can exercise decoder-driven UI.
+
+Verified 2026-09-30: unit tests (`tests/warmup_logic.test.js`) cover seen-since-start, a passing before the warm-up not counting, drivers without a transponder, unknown transponders newest-first with owner names, repeat counting and the size bound, and the countdown. `tests/browser_warmup.js` drives it with real decoder frames: Anna and Bo go green, Cia (registered wrong) stays missing until the unknown transponder is linked from the panel - then green and saved - preflight shows 3/3, and after a restarted warm-up Start warns naming the two not seen and starts the heat on confirm. While writing that test it first failed because a passing sent "before" the warm-up reached the page after the click and was (correctly) counted - a test timing issue, fixed by waiting for the frame to arrive. After that fix the same assertion still failed rarely (twice in about ten full-suite runs). Investigated with temporary logging: every run had exactly one decoder connection and the passing was processed before the start (`no_running_session` in the diagnostics), so it is not a duplicate-connection bug - but the flake could not be reproduced while logging (4/4 passed), so the root cause is unknown. The browser test now waits 750 ms between that passing and the start; the before/after rule itself is covered deterministically by the unit tests. 230 unit/integration tests pass, and the 46 browser scenarios passed three runs in a row.
+
 ## Documentation maintenance
 
 - [x] Update the architecture's module/dependency inventory as modules change.
diff --git a/docs/javascript-architecture.md b/docs/javascript-architecture.md
index c469354..15956e5 100644
--- a/docs/javascript-architecture.md
+++ b/docs/javascript-architecture.md
@@ -576,6 +576,14 @@ Type:
 Owns:
 - "Track layout: <label> - since <date> [New layout]" on Training stats, Race Day and the Dashboard; the button prompts for a name and calls the injected `addTrackLayout` (which refuses while a race session is running - `findRaceSessionBlockingLayoutChange` in `track_layouts_logic.js`)
 
+### `src/warmup_logic.js`
+Type:
+- pure warm-up / transponder check logic
+
+Owns:
+- `recordTransponderSighting`: in-memory, bounded map of transponder -> last seen (never persisted, never counted as laps); fed by `decoder_runtime.js`'s `onTransponderSeen` for every main-line passing, before the running-session check
+- `buildWarmupCheck`: per-heat entrant rows (seen since the warm-up started or not), unknown transponders with owner names; used by the Race Day warm-up panel (`race_day_view.js`) via `getRaceDayWarmupCheck` in `app.js`, which also owns the warm-up timer and its `warmup_*` voice events
+
 ### `src/misc_views.js`
 Type:
 - misc page renderers
diff --git a/package-lock.json b/package-lock.json
index 8e5cc7d..e0abbb7 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "rc-racecore",
-  "version": "1.25.0",
+  "version": "1.26.0",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "rc-racecore",
-      "version": "1.25.0",
+      "version": "1.26.0",
       "hasInstallScript": true,
       "dependencies": {
         "better-sqlite3": "^12.11.1",
diff --git a/package.json b/package.json
index 9fed52d..875c1c6 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "rc-racecore",
-  "version": "1.25.0",
+  "version": "1.26.0",
   "private": true,
   "description": "RC RaceCore live timing and race control with AMMC ingest and SQLite persistence",
   "engines": {
diff --git a/rc-race-sound-pack/sound_manifest.json b/rc-race-sound-pack/sound_manifest.json
index 0478287..fc4952d 100644
--- a/rc-race-sound-pack/sound_manifest.json
+++ b/rc-race-sound-pack/sound_manifest.json
@@ -47,6 +47,9 @@
       "race_1_minute": "Race starts in one minute.", "race_30_seconds": "Thirty seconds to start.", "race_10_seconds": "Ten seconds to start.",
       "drivers_ready": "Drivers, stand by.", "start_sequence": "Starting on the sound of the tone.", "false_start": "False start.", "restart_race": "Prepare to restart the race.",
       "staggered_release": "Car {tp}.",
+      "warmup_start": "Warm-up has started. {minutes} minutes.",
+      "warmup_1_minute": "One minute of warm-up remaining.",
+      "warmup_end": "Warm-up is over. Drivers to the grid.",
       "personal_best": "Personal best. {driverName}. {lapTime}.", "fastest_lap": "Fastest lap. {driverName}. {lapTime}.",
       "training_stable_pace": "{driverName}, good pace and consistent driving.",
       "track_record": "New track record. {driverName}. {lapTime}.", "new_leader": "New race leader. {driverName}.",
@@ -69,6 +72,9 @@
       "race_1_minute": "Start om en minut.", "race_30_seconds": "Trettio sekunder till start.", "race_10_seconds": "Tio sekunder till start.",
       "drivers_ready": "Förare, gör er redo.", "start_sequence": "Start på signalen.", "false_start": "Felaktig start.", "restart_race": "Förbered omstart.",
       "staggered_release": "Bil {tp}.",
+      "warmup_start": "Uppvärmningen har startat. {minutes} minuter.",
+      "warmup_1_minute": "En minut kvar av uppvärmningen.",
+      "warmup_end": "Uppvärmningen är slut. Förarna till start.",
       "personal_best": "Personbästa. {driverName}. {lapTime}.", "fastest_lap": "Snabbaste varv. {driverName}. {lapTime}.",
       "training_stable_pace": "{driverName}, bra tempo och stabil körning.",
       "track_record": "Nytt banrekord. {driverName}. {lapTime}.", "new_leader": "Ny ledare. {driverName}.",
diff --git a/src/app.js b/src/app.js
index 7d6170b..88f5eeb 100644
--- a/src/app.js
+++ b/src/app.js
@@ -4,8 +4,10 @@ import { escapeHtml } from "./html_escape.js";
 import { getOverlayModeLabel, buildOverlayPanels, renderOverlaySidePanel, renderOverlayLeaderboard, renderTeamOverlay, renderObsOverlay } from "./overlays.js";
 
 import { renderSettings } from "./settings.js";
-import { buildRaceDayQueue, buildRaceDayPreflight } from "./race_day_logic.js";
-import { renderRaceDayView } from "./race_day_view.js";
+import { buildRaceDayQueue, buildRaceDayPreflight, getRaceDriverIds } from "./race_day_logic.js";
+import { recordTransponderSighting, buildWarmupCheck } from "./warmup_logic.js";
+import { findTransponderConflict, getDriverProfileId } from "./driver_profile_logic.js";
+import { renderRaceDayView, refreshRaceDayWarmup } from "./race_day_view.js";
 import { beginSession as beginSessionControl, finishSession as finishSessionControl, pauseSession as pauseSessionControl, resumeSession as resumeSessionControl } from "./session_control.js";
 import { RACE_AUDIO_EVENT_DEFINITIONS, createRaceAudioEngine, normalizeRaceAudioSettings } from "./race_audio.js";
 
@@ -239,6 +241,55 @@ const disconnectDecoder = (options = {}) => disconnectDecoderHelper(options, {
   updateConnectionBadge,
 });
 const getTrackRecordMs = (session) => getTrackRecordMsLogic(session, { state });
+// Pre-heat warm-up / transponder check. Sightings are kept in memory only (never saved):
+// they just answer "has this transponder crossed the line since the warm-up started".
+const transponderSightings = new Map();
+let raceDayWarmup = null;
+const onTransponderSeen = (transponder) => {
+  recordTransponderSighting(transponderSightings, transponder, Date.now());
+  if (raceDayWarmup && currentView === "race_day") refreshRaceDayWarmup();
+};
+function stopRaceDayWarmup() {
+  (raceDayWarmup?.timers || []).forEach((timer) => clearTimeout(timer));
+  if (raceDayWarmup) raceDayWarmup = { ...raceDayWarmup, timers: [], stopped: true };
+}
+function startRaceDayWarmup(session, durationMs) {
+  stopRaceDayWarmup();
+  const minutes = Math.round(durationMs / 60000);
+  const warmup = { sessionId: session.id, startedAt: Date.now(), durationMs, timers: [] };
+  triggerRaceAudio("warmup_start", { interrupt: true, variables: { minutes }, logData: { sessionId: session.id } });
+  if (durationMs > 60000) warmup.timers.push(setTimeout(() => triggerRaceAudio("warmup_1_minute", { logData: { sessionId: session.id } }), durationMs - 60000));
+  warmup.timers.push(setTimeout(() => {
+    triggerRaceAudio("warmup_end", { interrupt: true, logData: { sessionId: session.id } });
+    if (currentView === "race_day") refreshRaceDayWarmup();
+  }, durationMs));
+  raceDayWarmup = warmup;
+}
+function getRaceDayWarmupCheck(session) {
+  if (!session) return null;
+  const byId = new Map(state.drivers.map((driver) => [driver.id, driver]));
+  const entrantIds = getRaceDriverIds(state, session);
+  const gridOrder = getSessionGridOrder(session).filter((id) => entrantIds.includes(id));
+  const ordered = [...gridOrder, ...entrantIds.filter((id) => !gridOrder.includes(id))];
+  const warmup = raceDayWarmup?.sessionId === session.id ? raceDayWarmup : null;
+  return {
+    warmup,
+    ...buildWarmupCheck({ entrants: ordered.map((id) => byId.get(id)).filter(Boolean), drivers: state.drivers, sightings: transponderSightings, since: warmup ? warmup.startedAt : Number.POSITIVE_INFINITY }),
+  };
+}
+// Quick fix from the warm-up panel: warns (like the Drivers page) if another person
+// already uses that transponder, then saves it on the driver straight away.
+function setDriverTransponder(driverId, transponder) {
+  const value = String(transponder || "").trim();
+  const driver = state.drivers.find((item) => item.id === driverId);
+  if (!driver || !value) return false;
+  const conflict = findTransponderConflict(state.drivers, { transponder: value, profileId: getDriverProfileId(driver), excludeDriverId: driver.id });
+  if (conflict && !window.confirm(t("warmup.transponder_conflict", { transponder: value, name: conflict.name }))) return false;
+  driver.transponder = value;
+  saveState();
+  return true;
+}
+
 const processDecoderMessage = (msg, decoderRole = "main") => processDecoderMessageHelper(msg, {
   state,
   t,
@@ -258,6 +309,7 @@ const processDecoderMessage = (msg, decoderRole = "main") => processDecoderMessa
   lastOverlayBestLapByKey,
   triggerRaceAudio,
   getTrackRecordMs,
+  onTransponderSeen,
 }, decoderRole);
 const renderDashboard = () => renderDashboardView({ addTrackLayout, state, dom, t, backend, getActiveSession, getStatusLabel, getSessionTypeLabel, getEventName, getModeLabel, getBackendUrl, formatLap, renderSessionsTable, setCurrentView: (view) => { currentView = view; }, updateViewUrl, renderNav, renderView, connectDecoder, disconnectDecoder, openOverlayWindow, ensureAudioContext, playPassingBeep, playFinishSiren, escapeHtml });
 const renderClasses = () => renderClassesView({ state, dom, t, selectedClassEditId: () => selectedClassEditId, setSelectedClassEditId: (value) => { selectedClassEditId = value; }, uid, saveState, renderView, renderTable, escapeHtml, setFormError, bindModalShell });
@@ -265,6 +317,7 @@ const renderDrivers = () => renderDriversView({ state, dom, t, driverBrandFilter
 const renderCars = () => renderCarsView({ state, dom, t, carBrandFilter: () => carBrandFilter, setCarBrandFilter: (value) => { carBrandFilter = value; }, selectedCarEditId: () => selectedCarEditId, setSelectedCarEditId: (value) => { selectedCarEditId = value; }, uid, saveState, renderView, renderTable, escapeHtml, setFormError, bindModalShell, normalizeCar });
 const renderGuide = () => renderGuideView({ dom, t });
 const renderRaceDay = () => renderRaceDayView({
+  getRaceDayWarmupCheck, startRaceDayWarmup, stopRaceDayWarmup, setDriverTransponder,
   addTrackLayout, renderView, state, dom, t, escapeHtml, formatLap, formatCountdown, formatElapsedClock,
   getEventName, getSessionTypeLabel, getStatusLabel, getStartModeLabel,
   getSessionTiming, getSessionGridEntries, buildRaceDayQueue, buildRaceDayPreflight,
@@ -1064,6 +1117,22 @@ const TRANSLATIONS = {
     "guide.tab_run": "Köra ett race",
     "guide.tab_training": "Träning & resultat",
     "guide.tab_videos": "Videoguider",
+    "warmup.title": "Uppvärmning / transponderkontroll",
+    "warmup.hint": "Starta uppvärmningen och låt alla köra över linjen. Grön bock = transpondern har setts. Saknas någon kan du byta transponder direkt här, eller koppla en okänd transponder som just passerat.",
+    "warmup.start": "Starta uppvärmning",
+    "warmup.restart": "Starta om uppvärmning",
+    "warmup.stop": "Avsluta uppvärmning",
+    "warmup.minutes": "{minutes} min",
+    "warmup.ended": "Uppvärmningen är slut - kontrollera bockarna och starta heatet.",
+    "warmup.seen_count": "{seen} av {total} sedda",
+    "warmup.no_transponder": "Ingen transponder",
+    "warmup.assign_unknown": "Koppla okänd transponder...",
+    "warmup.new_transponder": "Ny transponder",
+    "warmup.save": "Spara",
+    "warmup.unknown_seen": "Okända transpondrar som passerat",
+    "warmup.start_missing": "Har inte passerat under uppvärmningen: {names}. Starta ändå?",
+    "warmup.transponder_conflict": "Transponder {transponder} används redan av {name}. Spara ändå?",
+    "race_day.check_transponder_check": "Transponderkontroll",
     "layouts.bar_current": "Banlayout: {label} - sedan {date}",
     "layouts.bar_none": "Ingen banlayout satt ännu",
     "layouts.new": "Ny layout",
@@ -1856,6 +1925,7 @@ const TRANSLATIONS = {
     "guide.race_day_7": "7. Session replay i Tidtagning spelar upp sparade passeringar i ett isolerat testläge. Välj session, ladda och kör i 1x, 2x, 5x eller 10x utan att ändra originalresultat eller träningsstatistik.",
     "guide.race_day_8": "8. Redan när du registrerar eller ändrar en förare under Förare varnar systemet om transpondern redan används av en annan förare (t.ex. i fel klass) och namnger vem - ett komplement till förkontrollens kontroll av dubbla transpondrar inom samma heat. Samma person som kör flera klasser med sin egen transponder flaggas aldrig.",
     "guide.race_day_9": "9. Kör ni på ett nät där fler har åtkomst (t.ex. arenans WiFi)? Slå på Admin-PIN under Inställningar -> System & backup. Då kräver alla ändringar PIN - resultat, inställningar och uppdatering - medan visning och publika overlay-/träningslänkar fungerar som vanligt. Varje webbläsare loggar in en gång och kommer ihåg det i 30 dagar.",
+    "guide.race_day_10": "10. Transponderkontroll före heatet: välj heatet på Race Day och tryck Starta uppvärmning (1-3 min, med utrop). Varje förare får grön bock när transpondern passerat. Saknas någon, byt transponder direkt i panelen eller välj en av de okända transpondrarna som passerat - vanligaste felet är att någon registrerat fel nummer. Start varnar om någon inte setts men går att starta ändå.",
     "guide.dashboard_title": "Schemaavvikelse på Översikt",
     "guide.dashboard_1": "Översikt visar nu skillnaden mellan planerad tid och faktisk körtid för alla startade sessioner.",
     "guide.dashboard_2": "Planerad tid räknar sessionstid plus follow-up. Faktisk tid räknar verklig tid från start till stopp eller nuvarande tid om heatet fortfarande kör.",
@@ -2674,6 +2744,22 @@ const TRANSLATIONS = {
     "guide.tab_run": "Run a race",
     "guide.tab_training": "Training & results",
     "guide.tab_videos": "Video guides",
+    "warmup.title": "Warm-up / transponder check",
+    "warmup.hint": "Start the warm-up and let everyone cross the line. Green tick = the transponder has been seen. If someone is missing, change their transponder right here, or link an unknown transponder that just crossed.",
+    "warmup.start": "Start warm-up",
+    "warmup.restart": "Restart warm-up",
+    "warmup.stop": "End warm-up",
+    "warmup.minutes": "{minutes} min",
+    "warmup.ended": "Warm-up is over - check the ticks and start the heat.",
+    "warmup.seen_count": "{seen} of {total} seen",
+    "warmup.no_transponder": "No transponder",
+    "warmup.assign_unknown": "Link unknown transponder...",
+    "warmup.new_transponder": "New transponder",
+    "warmup.save": "Save",
+    "warmup.unknown_seen": "Unknown transponders that crossed",
+    "warmup.start_missing": "Not seen during warm-up: {names}. Start anyway?",
+    "warmup.transponder_conflict": "Transponder {transponder} is already used by {name}. Save anyway?",
+    "race_day.check_transponder_check": "Transponder check",
     "layouts.bar_current": "Track layout: {label} - since {date}",
     "layouts.bar_none": "No track layout set yet",
     "layouts.new": "New layout",
@@ -3466,6 +3552,7 @@ const TRANSLATIONS = {
     "guide.race_day_7": "7. Session replay in Timing replays saved passings in an isolated test mode. Select a session, load it, and run at 1x, 2x, 5x, or 10x without modifying source results or training statistics.",
     "guide.race_day_8": "8. Already when you register or edit a driver under Drivers, the system warns if the transponder is already used by a different driver (e.g. in the wrong class) and names who - a complement to the preflight's duplicate-transponder check within a single heat. The same person racing multiple classes on their own transponder is never flagged.",
     "guide.race_day_9": "9. Running on a network others can reach (e.g. the venue WiFi)? Turn on the Admin PIN under Settings -> System & backup. Every change then needs the PIN - results, settings and updates - while viewing and public overlay/training links work as usual. Each browser logs in once and is remembered for 30 days.",
+    "guide.race_day_10": "10. Transponder check before the heat: select the heat on Race Day and press Start warm-up (1-3 min, with announcements). Each driver gets a green tick once their transponder has crossed. If someone is missing, change their transponder right in the panel or pick one of the unknown transponders that crossed - the most common mistake is a wrongly registered number. Start warns if someone wasn't seen, but can still start.",
     "guide.dashboard_title": "Schedule drift on overview",
     "guide.dashboard_1": "Overview now shows the difference between planned time and actual elapsed time for all started sessions.",
     "guide.dashboard_2": "Planned time includes session duration plus follow-up. Actual time uses real time from start to stop, or the current time if the heat is still running.",
diff --git a/src/decoder_runtime.js b/src/decoder_runtime.js
index cf46079..9f89760 100644
--- a/src/decoder_runtime.js
+++ b/src/decoder_runtime.js
@@ -275,6 +275,7 @@ export function processDecoderMessageHelper(msg, deps, decoderRole = "main") {
     findEventTeamForPassing, persistPassingToBackend, pushOverlayEvent, buildLeaderboard,
     formatLap, announcePassing, saveState, lastOverlayLeaderKeyBySession,
     lastOverlayTop3BySession, lastOverlayBestLapByKey, triggerRaceAudio = () => {}, getTrackRecordMs = () => null,
+    onTransponderSeen = () => {},
   } = deps;
 
   const report = (reason, outcome) => decoderDiagnostics.message(decoderRole, msg, reason, outcome);
@@ -289,6 +290,14 @@ export function processDecoderMessageHelper(msg, deps, decoderRole = "main") {
     return;
   }
 
+  // Noted before the running-session check on purpose: the pre-heat warm-up / transponder
+  // check needs to see passings while the heat hasn't started yet. Main line only, the
+  // same line that counts laps.
+  if (decoderRole === "main") {
+    const seenTransponder = String(msg.transponder ?? msg.tran_code ?? "").replace("ID:", "").trim();
+    if (seenTransponder) onTransponderSeen(seenTransponder);
+  }
+
   const session = getActiveSession();
   if (!session || session.status !== "running") {
     report("no_running_session");
diff --git a/src/misc_views.js b/src/misc_views.js
index 72f9f7b..bff50fc 100644
--- a/src/misc_views.js
+++ b/src/misc_views.js
@@ -97,7 +97,7 @@ export function renderGuideView({ dom, t }) {
 
     <div data-guide-panel="run">
       <div class="guide-section-grid mt-16">
-        ${renderGuidePanel("guide.race_day_title", ["guide.race_day_1", "guide.race_day_2", "guide.race_day_3", "guide.race_day_4", "guide.race_day_5", "guide.race_day_6", "guide.race_day_7", "guide.race_day_8", "guide.race_day_9"], "", { t })}
+        ${renderGuidePanel("guide.race_day_title", ["guide.race_day_1", "guide.race_day_2", "guide.race_day_3", "guide.race_day_4", "guide.race_day_5", "guide.race_day_6", "guide.race_day_7", "guide.race_day_8", "guide.race_day_9", "guide.race_day_10"], "", { t })}
         ${renderGuidePanel("guide.manage_steps_title", ["guide.manage_steps_1", "guide.manage_steps_2", "guide.manage_steps_3", "guide.manage_steps_4", "guide.manage_steps_5", "guide.manage_steps_6", "guide.manage_steps_7", "guide.manage_steps_8", "guide.manage_steps_9"], "", { t })}
       </div>
 
diff --git a/src/race_audio.js b/src/race_audio.js
index 110b9ee..5450355 100644
--- a/src/race_audio.js
+++ b/src/race_audio.js
@@ -10,6 +10,7 @@ export const RACE_AUDIO_EVENT_DEFINITIONS = Object.freeze([
   event("start_tone", "start", "high", false, "effects/start_beep.wav"),
   event("false_start", "start", "critical", true, "effects/warning.wav", 1000), event("restart_race", "start", "high"),
   event("staggered_release", "start", "normal"),
+  event("warmup_start", "start", "normal"), event("warmup_1_minute", "start", "normal"), event("warmup_end", "start", "high"),
   event("transponder_pass", "race", "pass", false, "effects/transponder_pass.wav"), event("lap_completed", "race", "pass", false),
   event("personal_best", "race", "low", true, "effects/personal_best.wav", 1500),
   event("fastest_lap", "race", "normal", true, "effects/fastest_lap_trophy.wav", 1500),
diff --git a/src/race_day_logic.js b/src/race_day_logic.js
index 46804d1..885007c 100644
--- a/src/race_day_logic.js
+++ b/src/race_day_logic.js
@@ -12,7 +12,7 @@ function getEvent(state, session) {
   return state.events.find((event) => event.id === session?.eventId) || null;
 }
 
-function getRaceDriverIds(state, session, event) {
+export function getRaceDriverIds(state, session, event = getEvent(state, session)) {
   if (Array.isArray(session?.driverIds) && session.driverIds.length) {
     return unique(session.driverIds);
   }
diff --git a/src/race_day_view.js b/src/race_day_view.js
index 2cb195a..534b208 100644
--- a/src/race_day_view.js
+++ b/src/race_day_view.js
@@ -35,6 +35,7 @@ function renderPreflightDetail(item, { t, formatLap, escapeHtml }) {
   }
   if (item.id === "duplicate_transponders" && item.duplicates?.length) return escapeHtml(item.duplicates.join(", "));
   if (item.id === "duplicate_team_members" && item.duplicateTeamMemberNames?.length) return escapeHtml(item.duplicateTeamMemberNames.join(", "));
+  if (item.id === "transponder_check") return `${item.seen}/${item.total}`;
   if (item.id === "grid") return item.notRequired ? t("race_day.not_required") : `${item.count || 0}/${item.expectedCount || 0}`;
   return t(`race_day.check_${item.level}`);
 }
@@ -52,6 +53,107 @@ function renderQueueSession(session, positionKey, deps) {
     </article>`;
 }
 
+
+// --- Warm-up / transponder check -------------------------------------------------------
+// Shown for a selected, not-yet-started race-format heat with driver transponders. The panel
+// re-renders on its own (refreshRaceDayWarmup) on every passing, without rebuilding the page.
+let lastWarmupDeps = null;
+let warmupClockTimer = null;
+
+function showsWarmupPanel(session) {
+  return Boolean(session && session.status === "ready" && session.mode !== "track" && session.type !== "team_race" && !isPracticeSessionType(session.type));
+}
+
+function formatMmSs(ms) {
+  const total = Math.ceil(ms / 1000);
+  return `${Math.floor(total / 60)}:${String(total % 60).padStart(2, "0")}`;
+}
+
+function renderWarmupPanelInner({ t, escapeHtml, getRaceDayWarmupCheck }, session) {
+  const check = getRaceDayWarmupCheck(session);
+  const warmup = check.warmup;
+  const remaining = warmup && !warmup.stopped ? Math.max(0, warmup.startedAt + warmup.durationMs - Date.now()) : 0;
+  const unknownOptions = check.unknownTransponders.map((item) => `<option value="${escapeHtml(item.transponder)}">${escapeHtml(item.ownerName ? `${item.transponder} (${item.ownerName})` : item.transponder)}</option>`).join("");
+  const status = (row) => (!warmup ? "–" : row.seen ? "✅" : "⏳");
+  return `
+    <div class="panel-header">
+      <div><h3>${t("warmup.title")}</h3><p class="hint">${t("warmup.hint")}</p></div>
+      ${warmup ? `<span class="pill ${check.seenCount === check.total ? "pill-green" : "pill-warn"}">${t("warmup.seen_count", { seen: check.seenCount, total: check.total })}</span>` : ""}
+    </div>
+    <div class="panel-body">
+      <div class="actions">
+        ${warmup && remaining > 0
+          ? `<strong class="warmup-clock" data-warmup-clock>${formatMmSs(remaining)}</strong><button class="btn" type="button" data-warmup-stop>${t("warmup.stop")}</button>`
+          : `<select data-warmup-minutes>${[1, 2, 3].map((minutes) => `<option value="${minutes}" ${minutes === 2 ? "selected" : ""}>${t("warmup.minutes", { minutes })}</option>`).join("")}</select>
+             <button class="btn btn-primary" type="button" data-warmup-start>${t(warmup ? "warmup.restart" : "warmup.start")}</button>
+             ${warmup ? `<span class="hint">${t("warmup.ended")}</span>` : ""}`}
+      </div>
+      <table class="warmup-table mt-16">
+        <tbody>
+          ${check.rows.map((row) => `
+            <tr class="${warmup && !row.seen ? "is-missing" : ""}" data-warmup-driver="${escapeHtml(row.driverId)}">
+              <td class="warmup-status">${status(row)}</td>
+              <td><strong>${escapeHtml(row.name)}</strong><br><small>${escapeHtml(row.transponder || t("warmup.no_transponder"))}</small></td>
+              <td>${warmup && !row.seen ? `<div class="warmup-fix">
+                ${unknownOptions ? `<select data-warmup-assign><option value="">${t("warmup.assign_unknown")}</option>${unknownOptions}</select>` : ""}
+                <input data-warmup-transponder placeholder="${escapeHtml(t("warmup.new_transponder"))}" inputmode="numeric" />
+                <button class="btn btn-mini" type="button" data-warmup-save>${t("warmup.save")}</button></div>` : ""}</td>
+            </tr>`).join("")}
+        </tbody>
+      </table>
+      ${warmup && check.unknownTransponders.length ? `<p class="hint mt-16">${t("warmup.unknown_seen")}: ${check.unknownTransponders.map((item) => `<span class="pill">${escapeHtml(item.ownerName ? `${item.transponder} (${item.ownerName})` : item.transponder)}</span>`).join(" ")}</p>` : ""}
+    </div>`;
+}
+
+function bindWarmupPanel(panel, deps, session) {
+  const { startRaceDayWarmup, stopRaceDayWarmup, setDriverTransponder } = deps;
+  panel.querySelector("[data-warmup-start]")?.addEventListener("click", () => {
+    startRaceDayWarmup(session, Number(panel.querySelector("[data-warmup-minutes]")?.value || 2) * 60000);
+    refreshRaceDayWarmup(true);
+  });
+  panel.querySelector("[data-warmup-stop]")?.addEventListener("click", () => {
+    stopRaceDayWarmup();
+    refreshRaceDayWarmup(true);
+  });
+  panel.querySelectorAll("[data-warmup-driver]").forEach((row) => {
+    const driverId = row.dataset.warmupDriver;
+    row.querySelector("[data-warmup-assign]")?.addEventListener("change", (event) => {
+      if (event.target.value && setDriverTransponder(driverId, event.target.value)) refreshRaceDayWarmup(true);
+    });
+    row.querySelector("[data-warmup-save]")?.addEventListener("click", () => {
+      if (setDriverTransponder(driverId, row.querySelector("[data-warmup-transponder]")?.value)) refreshRaceDayWarmup(true);
+    });
+  });
+  clearInterval(warmupClockTimer);
+  warmupClockTimer = setInterval(() => {
+    if (!panel.isConnected) { clearInterval(warmupClockTimer); return; }
+    const clock = panel.querySelector("[data-warmup-clock]");
+    if (!clock) return;
+    const warmup = deps.getRaceDayWarmupCheck(session).warmup;
+    const remaining = warmup ? Math.max(0, warmup.startedAt + warmup.durationMs - Date.now()) : 0;
+    clock.textContent = formatMmSs(remaining);
+    if (remaining <= 0) refreshRaceDayWarmup(true);
+  }, 500);
+}
+
+function paintWarmupPanel() {
+  const panel = document.getElementById("raceDayWarmup");
+  if (!panel || !lastWarmupDeps) return;
+  const session = lastWarmupDeps.getSession();
+  if (!showsWarmupPanel(session)) return;
+  panel.innerHTML = renderWarmupPanelInner(lastWarmupDeps, session);
+  bindWarmupPanel(panel, lastWarmupDeps, session);
+}
+
+// Re-renders the whole Race Day page (a few ms) so the panel and the preflight row stay in
+// step. On a passing (force = false) it waits while the operator is typing in any field,
+// so a half-entered transponder or lap window is never wiped.
+export function refreshRaceDayWarmup(force = false) {
+  if (!lastWarmupDeps || !document.getElementById("raceDayWarmup")) return;
+  if (!force && ["INPUT", "SELECT", "TEXTAREA"].includes(document.activeElement?.tagName)) return;
+  lastWarmupDeps.renderView();
+}
+
 export function renderRaceDayView(deps) {
   const {
     state, dom, t, escapeHtml, formatLap, formatCountdown, formatElapsedClock,
@@ -59,11 +161,16 @@ export function renderRaceDayView(deps) {
     getSessionTiming, getSessionGridEntries, buildRaceDayQueue, buildRaceDayPreflight,
     backendAvailable, selectSession, startSession, finishSession, pauseSession, resumeSession,
     saveLapWindow, navigateTo, getStartLightState, addTrackLayout, renderView,
+    getRaceDayWarmupCheck, startRaceDayWarmup, stopRaceDayWarmup, setDriverTransponder,
   } = deps;
   const queue = buildRaceDayQueue(state);
   const session = queue.current;
   const preflight = buildRaceDayPreflight(state, session, { backendAvailable });
-  const checks = sortRaceDayChecks(preflight.checks);
+  const warmupForChecks = showsWarmupPanel(session) ? getRaceDayWarmupCheck(session) : null;
+  const checks = sortRaceDayChecks([
+    ...preflight.checks,
+    ...(warmupForChecks?.warmup ? [{ id: "transponder_check", level: warmupForChecks.missing.length ? "warning" : "ok", seen: warmupForChecks.seenCount, total: warmupForChecks.total }] : []),
+  ]);
   const blockers = checks.filter((item) => item.level === "error").length;
   const warnings = checks.filter((item) => item.level === "warning").length;
   const lapWindowCheck = preflight.checks.find((item) => item.id === "lap_window") || null;
@@ -113,6 +220,8 @@ export function renderRaceDayView(deps) {
           </div>
         </section>
 
+        ${showsWarmupPanel(session) ? `<section class="panel mt-16" id="raceDayWarmup"></section>` : ""}
+
         <section class="panel">
           <div class="panel-header"><h3>${t("race_day.start_list")}</h3><span class="pill">${grid.length}</span></div>
           <div class="panel-body race-day-grid-list">
@@ -185,8 +294,15 @@ export function renderRaceDayView(deps) {
     saveLapWindow(session, minLapSec, maxLapSec);
   });
   bindTrackLayoutBar(dom.view, { state, t, addTrackLayout, renderView });
+  lastWarmupDeps = { t, escapeHtml, renderView, getRaceDayWarmupCheck, startRaceDayWarmup, stopRaceDayWarmup, setDriverTransponder, getSession: () => buildRaceDayQueue(state).current };
+  paintWarmupPanel();
   document.getElementById("raceDayStart")?.addEventListener("click", async () => {
     if (!session || !preflight.ready) return;
+    // Warns (never blocks - a driver may not show up) when the warm-up ran and someone in
+    // the heat still hasn't crossed the line.
+    const warmupCheck = showsWarmupPanel(session) ? getRaceDayWarmupCheck(session) : null;
+    if (warmupCheck?.warmup && warmupCheck.missing.length && !window.confirm(t("warmup.start_missing", { names: warmupCheck.missing.map((row) => row.name).join(", ") }))) return;
+    stopRaceDayWarmup();
     if (!isSelected) selectSession(session.id, { render: false });
     const button = document.getElementById("raceDayStart");
     if (button) button.disabled = true;
diff --git a/src/styles.css b/src/styles.css
index 8c80ea1..4cdd830 100644
--- a/src/styles.css
+++ b/src/styles.css
@@ -4447,3 +4447,45 @@ select:focus {
   font-size: 0.86rem;
   color: var(--muted, inherit);
 }
+
+.warmup-clock {
+  font-size: 1.6rem;
+  font-variant-numeric: tabular-nums;
+  margin-right: 8px;
+}
+
+.warmup-table {
+  width: 100%;
+  border-collapse: collapse;
+}
+
+.warmup-table td {
+  padding: 8px 6px;
+  border-top: 1px solid var(--line);
+  vertical-align: middle;
+}
+
+.warmup-status {
+  width: 2.2em;
+  text-align: center;
+  font-size: 1.2rem;
+}
+
+.warmup-table tr.is-missing td {
+  background: color-mix(in srgb, var(--accent) 8%, transparent);
+}
+
+.warmup-fix {
+  display: flex;
+  flex-wrap: wrap;
+  gap: 6px;
+  justify-content: flex-end;
+}
+
+.warmup-fix input {
+  width: 10em;
+}
+
+#raceDayWarmup .panel-header .pill {
+  white-space: nowrap;
+}
diff --git a/src/warmup_logic.js b/src/warmup_logic.js
new file mode 100644
index 0000000..f2b905e
--- /dev/null
+++ b/src/warmup_logic.js
@@ -0,0 +1,45 @@
+// Warm-up / transponder check before a heat: every passing the main decoder sees is
+// remembered (transponder -> when), independent of whether a session is running, so the
+// Race Day panel can show which drivers in the selected heat have been seen since the
+// warm-up started and which unknown transponders crossed the line.
+const MAX_SIGHTINGS = 500;
+
+export function recordTransponderSighting(sightings, transponder, at = Date.now()) {
+  const key = String(transponder || "").trim();
+  if (!key) return sightings;
+  const previous = sightings.get(key);
+  sightings.delete(key); // re-insert so Map order stays oldest -> newest
+  sightings.set(key, { transponder: key, lastSeenAt: at, count: (previous?.count || 0) + 1 });
+  while (sightings.size > MAX_SIGHTINGS) sightings.delete(sightings.keys().next().value);
+  return sightings;
+}
+
+// entrants: drivers in the heat, in start order. drivers: every registered driver, used to
+// name the owner of a transponder that crossed the line but doesn't belong to this heat.
+export function buildWarmupCheck({ entrants = [], drivers = [], sightings = new Map(), since = 0 }) {
+  const seenSince = (transponder) => {
+    const sighting = transponder ? sightings.get(String(transponder).trim()) : null;
+    return sighting && sighting.lastSeenAt >= since ? sighting : null;
+  };
+  const rows = entrants.map((driver) => {
+    const sighting = seenSince(driver.transponder);
+    return { driverId: driver.id, name: driver.name, transponder: String(driver.transponder || ""), seen: Boolean(sighting), lastSeenAt: sighting?.lastSeenAt || null };
+  });
+  const entrantTransponders = new Set(rows.map((row) => row.transponder).filter(Boolean));
+  const unknownTransponders = [...sightings.values()]
+    .filter((sighting) => sighting.lastSeenAt >= since && !entrantTransponders.has(sighting.transponder))
+    .map((sighting) => ({ ...sighting, ownerName: drivers.find((driver) => String(driver.transponder || "") === sighting.transponder)?.name || "" }))
+    .sort((a, b) => b.lastSeenAt - a.lastSeenAt);
+  return {
+    rows,
+    total: rows.length,
+    seenCount: rows.filter((row) => row.seen).length,
+    missing: rows.filter((row) => !row.seen),
+    unknownTransponders,
+  };
+}
+
+export function getWarmupRemainingMs(warmup, now = Date.now()) {
+  if (!warmup?.startedAt) return 0;
+  return Math.max(0, warmup.startedAt + warmup.durationMs - now);
+}
diff --git a/tests/browser_fake_decoder.js b/tests/browser_fake_decoder.js
index 5262610..ba64573 100644
--- a/tests/browser_fake_decoder.js
+++ b/tests/browser_fake_decoder.js
@@ -12,8 +12,7 @@ export async function freePort() {
 
 // Accepts the WebSocket upgrade handshake so the frontend's real decoder-connect path
 // (src/decoder_runtime.js) reaches `connected: true` without a physical AMMC decoder.
-// No frames are sent or parsed: scenarios using this only need an established socket,
-// not lap data.
+// sendPassing() pushes a PASSING frame for scenarios that need the app to see a transponder.
 export async function startFakeDecoder() {
   const port = await freePort();
   const server = createServer();
@@ -40,6 +39,14 @@ export async function startFakeDecoder() {
     // handshake) to simulate a decoder/network interruption, while the server keeps
     // listening so the frontend's own reconnect logic has somewhere to reconnect to.
     dropConnections: () => { for (const socket of sockets) socket.destroy(); },
+    // Sends an AMMC-style PASSING message as an unmasked server->client WebSocket text frame.
+    sendPassing: (transponder) => {
+      const payload = Buffer.from(JSON.stringify({ msg: "PASSING", transponder: String(transponder), rtc_time: new Date().toISOString() }));
+      const header = payload.length < 126
+        ? Buffer.from([0x81, payload.length])
+        : Buffer.from([0x81, 126, payload.length >> 8, payload.length & 0xff]);
+      for (const socket of sockets) socket.write(Buffer.concat([header, payload]));
+    },
     close: () => new Promise(resolve => {
       for (const socket of sockets) socket.destroy();
       server.close(() => resolve());
diff --git a/tests/browser_smoke.js b/tests/browser_smoke.js
index f21c3b5..0da9c08 100644
--- a/tests/browser_smoke.js
+++ b/tests/browser_smoke.js
@@ -10,6 +10,7 @@ import { runGuideTabsSmoke } from "./browser_guide_tabs.js";
 import { runAuthSmoke } from "./browser_auth.js";
 import { runTtsSettingsSmoke } from "./browser_tts_settings.js";
 import { runTrackLayoutsSmoke } from "./browser_track_layouts.js";
+import { runWarmupSmoke } from "./browser_warmup.js";
 import { runObsPopupSmoke } from "./browser_obs_popup.js";
 import { runDecoderReconnectSmoke } from "./browser_decoder_reconnect.js";
 import assert from "node:assert/strict";
@@ -150,6 +151,7 @@ try {
   await runAuthSmoke({ evaluate, navigate, fill, savedState, waitFor });
   await runTtsSettingsSmoke({ evaluate, navigate, savedState, waitFor });
   await runTrackLayoutsSmoke({ evaluate, navigate, savedState, waitFor, base, dialogs });
+  await runWarmupSmoke({ evaluate, navigate, savedState, waitFor, base, dialogs });
   await runRaceDaySmoke({ evaluate, navigate, fill, savedState, waitFor, pause, base, dialogs });
   await runRaceDayStartSequencesSmoke({ evaluate, navigate, waitFor, pause, base, dialogs });
   await runObsPopupSmoke({ evaluate, navigate, fill, savedState, waitFor, pause, base, debugPort, dialogs, realClick });
diff --git a/tests/browser_warmup.js b/tests/browser_warmup.js
new file mode 100644
index 0000000..82e5a91
--- /dev/null
+++ b/tests/browser_warmup.js
@@ -0,0 +1,84 @@
+import assert from "node:assert/strict";
+import { startFakeDecoder } from "./browser_fake_decoder.js";
+
+// Pre-heat warm-up / transponder check, driven through real decoder passings: drivers go
+// green as their transponder crosses, a driver registered with the wrong number gets the
+// unknown transponder linked straight from the panel, and Start warns about anyone missing.
+export async function runWarmupSmoke({ evaluate, navigate, savedState, waitFor, base, dialogs }) {
+  const patchState = async (patch) => {
+    const current = await savedState();
+    Object.assign(current, patch);
+    const response = await fetch(base + "/api/state", { method: "POST", headers: { "Content-Type": "application/json" }, body: JSON.stringify(current) });
+    assert.equal(response.ok, true);
+  };
+  const statuses = () => evaluate(`Object.fromEntries([...document.querySelectorAll("[data-warmup-driver]")].map((row) => [row.querySelector("strong").textContent, row.querySelector(".warmup-status").textContent.trim()]))`);
+
+  const dialogsAtStart = dialogs.length;
+  const decoder = await startFakeDecoder();
+  const classId = "wu_class";
+  const drivers = [
+    { id: "wu_a", name: "WU Anna", classId, transponder: "8110001" },
+    { id: "wu_b", name: "WU Bo", classId, transponder: "8110002" },
+    { id: "wu_c", name: "WU Cia", classId, transponder: "8110003" }, // registered with the wrong number
+  ];
+  const event = { id: "wu_event", name: "WU Race", classId, mode: "race", raceConfig: { minLapMs: 3000, maxLapMs: 60000 } };
+  const heat = { id: "wu_heat", eventId: event.id, name: "WU Heat 1", type: "heat", durationMin: 5, status: "ready" };
+  const seeded = await savedState();
+  await patchState({
+    classes: [...seeded.classes, { id: classId, name: "WU Class" }],
+    drivers: [...seeded.drivers, ...drivers],
+    events: [...seeded.events, event],
+    sessions: [...seeded.sessions.map((session) => (["running", "paused"].includes(session.status) ? { ...session, status: "finished" } : session)), heat],
+    activeSessionId: heat.id,
+    settings: { ...seeded.settings, autoReconnect: true, wsUrl: `ws://127.0.0.1:${decoder.port}`, raceAudio: { ...seeded.settings.raceAudio, enabled: false } },
+  });
+
+  try {
+    await navigate("race_day", "raceDayStart");
+    await waitFor(async () => evaluate('document.getElementById("connectionBadge")?.classList.contains("badge-online")'), "decoder connected");
+    await waitFor(async () => Boolean(await evaluate(`document.querySelector("[data-warmup-start]")`)), "warm-up panel shown for a ready heat");
+
+    decoder.sendPassing("8110001"); // before the warm-up starts - must not count
+    // Wait for the frame to actually reach the page (decoder diagnostics count it) before
+    // starting the warm-up, otherwise it could arrive after the start and rightly count.
+    await waitFor(async () => evaluate(`import("/src/decoder_diagnostics.js").then(({ decoderDiagnostics }) => JSON.stringify(decoderDiagnostics.snapshot?.() || decoderDiagnostics).includes("8110001"))`), "pre-warm-up passing received");
+    // Rare flake seen twice in ~10 suite runs (not reproducible with extra logging): the
+    // passing counted as after the start. A short settle keeps this scenario about the UI;
+    // the before/after rule itself is covered deterministically in warmup_logic.test.js.
+    await new Promise((resolve) => setTimeout(resolve, 750));
+    await evaluate(`(() => { document.querySelector("[data-warmup-minutes]").value = "1"; document.querySelector("[data-warmup-start]").click(); })()`);
+    await waitFor(async () => Boolean(await evaluate(`document.querySelector("[data-warmup-clock]")`)), "countdown running");
+    assert.deepEqual(await statuses(), { "WU Anna": "⏳", "WU Bo": "⏳", "WU Cia": "⏳" }, "a passing from before the warm-up doesn't count");
+
+    decoder.sendPassing("8110001");
+    decoder.sendPassing("8110002");
+    decoder.sendPassing("8119999"); // Cia's real transponder
+    await waitFor(async () => JSON.stringify(await statuses()) === JSON.stringify({ "WU Anna": "✅", "WU Bo": "✅", "WU Cia": "⏳" }), "Anna and Bo go green, Cia still missing");
+    console.log("PASS drivers go green as their transponder crosses during the warm-up");
+
+    await evaluate(`(() => { const select = document.querySelector('[data-warmup-driver="wu_c"] [data-warmup-assign]'); select.value = "8119999"; select.dispatchEvent(new Event("change")); })()`);
+    await waitFor(async () => (await statuses())["WU Cia"] === "✅", "Cia green after linking the unknown transponder");
+    await waitFor(async () => (await savedState()).drivers.find((driver) => driver.id === "wu_c").transponder === "8119999", "Cia's transponder saved");
+    assert.match(await evaluate(`document.body.innerText`), /Transponder check[\s\S]{0,40}3\/3/, "preflight shows the check as complete");
+    console.log("PASS an unknown transponder seen during the warm-up can be linked to a driver in one step");
+
+    await evaluate(`document.querySelector("[data-warmup-stop]").click()`);
+    await evaluate(`document.querySelector("[data-warmup-start]").click()`);
+    decoder.sendPassing("8110001");
+    await waitFor(async () => (await statuses())["WU Anna"] === "✅", "restarted warm-up sees Anna");
+    const before = dialogs.length;
+    await evaluate(`document.getElementById("raceDayStart").click()`);
+    await waitFor(async () => dialogs.slice(before).some((dialog) => dialog.type === "confirm" && /WU Bo/.test(dialog.message) && /WU Cia/.test(dialog.message)), "Start warns about the drivers not seen");
+    await waitFor(async () => (await savedState()).sessions.find((session) => session.id === heat.id)?.status === "running", "confirming starts the heat anyway");
+    console.log("PASS Start warns about drivers not seen during the warm-up but can still start the heat");
+  } finally {
+    dialogs.splice(dialogsAtStart);
+    const current = await savedState();
+    await patchState({
+      settings: { ...current.settings, autoReconnect: false },
+      sessions: current.sessions.map((session) => (session.id === heat.id ? { ...session, status: "finished", endedAt: Date.now() } : session)),
+      activeSessionId: "",
+    });
+    await decoder.close();
+  }
+}
diff --git a/tests/race_audio.test.js b/tests/race_audio.test.js
index 5cd3277..e78ba8b 100644
--- a/tests/race_audio.test.js
+++ b/tests/race_audio.test.js
@@ -124,7 +124,7 @@ test("cancelling a pending start prevents the official start callback", async ()
 test("event catalog covers every supported race-audio event", () => {
   const keys = new Set(RACE_AUDIO_EVENT_DEFINITIONS.map((item) => item.key));
   [
-    "grid_open", "grid_closed", "race_1_minute", "race_30_seconds", "race_10_seconds", "drivers_ready", "start_sequence", "start_tone", "false_start", "restart_race", "staggered_release",
+    "grid_open", "grid_closed", "race_1_minute", "race_30_seconds", "race_10_seconds", "drivers_ready", "start_sequence", "start_tone", "false_start", "restart_race", "staggered_release", "warmup_start", "warmup_1_minute", "warmup_end",
     "transponder_pass", "lap_completed", "personal_best", "fastest_lap", "track_record", "training_stable_pace", "new_leader", "position_gain", "position_loss", "final_lap", "one_minute_remaining", "thirty_seconds_remaining", "ten_seconds_remaining", "time_expired", "race_finished",
     "track_call", "track_clear", "yellow_flag", "red_flag", "race_paused", "race_resumed", "marshal_warning", "marshal_required", "penalty", "stop_and_go", "drive_through", "disqualified",
     "pit_lane_open", "pit_lane_closed", "entering_pits", "leaving_pits", "pit_speed_warning",
diff --git a/tests/run.js b/tests/run.js
index ce06d9a..d5b469a 100644
--- a/tests/run.js
+++ b/tests/run.js
@@ -1,4 +1,5 @@
 import "./auth.test.js";
+import "./warmup_logic.test.js";
 import "./tts.test.js";
 import "./piper_speech.test.js";
 import "./driver_profile_logic.test.js";
diff --git a/tests/warmup_logic.test.js b/tests/warmup_logic.test.js
new file mode 100644
index 0000000..4c5a025
--- /dev/null
+++ b/tests/warmup_logic.test.js
@@ -0,0 +1,52 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+import { recordTransponderSighting, buildWarmupCheck, getWarmupRemainingMs } from "../src/warmup_logic.js";
+
+const entrants = [
+  { id: "a", name: "Anna", transponder: "1001" },
+  { id: "b", name: "Bo", transponder: "1002" },
+  { id: "c", name: "Cia", transponder: "" },
+];
+
+test("a driver is green only once their transponder crosses after the warm-up started", () => {
+  const sightings = new Map();
+  recordTransponderSighting(sightings, "1001", 500); // before the warm-up - must not count
+  recordTransponderSighting(sightings, "1002", 1500);
+  let check = buildWarmupCheck({ entrants, sightings, since: 1000 });
+  assert.deepEqual(check.rows.map((row) => row.seen), [false, true, false]);
+  assert.equal(check.seenCount, 1);
+  assert.equal(check.total, 3);
+  assert.deepEqual(check.missing.map((row) => row.name), ["Anna", "Cia"], "a driver with no transponder is never green");
+  recordTransponderSighting(sightings, "1001", 2000);
+  check = buildWarmupCheck({ entrants, sightings, since: 1000 });
+  assert.equal(check.rows[0].seen, true);
+  assert.equal(check.rows[0].lastSeenAt, 2000);
+});
+
+test("unknown transponders are listed newest first, naming the owner if it belongs to another driver", () => {
+  const sightings = new Map();
+  recordTransponderSighting(sightings, "9999", 1100);
+  recordTransponderSighting(sightings, "7777", 1200);
+  recordTransponderSighting(sightings, "1001", 1300);
+  recordTransponderSighting(sightings, "5555", 900); // before the warm-up
+  const check = buildWarmupCheck({ entrants, drivers: [...entrants, { id: "x", name: "Xerxes", transponder: "7777" }], sightings, since: 1000 });
+  assert.deepEqual(check.unknownTransponders.map((item) => [item.transponder, item.ownerName]), [["7777", "Xerxes"], ["9999", ""]]);
+});
+
+test("sightings count repeat passings and stay bounded", () => {
+  const sightings = new Map();
+  recordTransponderSighting(sightings, " 42 ", 1);
+  recordTransponderSighting(sightings, "42", 2);
+  assert.equal(sightings.get("42").count, 2);
+  recordTransponderSighting(sightings, "", 3);
+  assert.equal(sightings.size, 1);
+  for (let i = 0; i < 600; i += 1) recordTransponderSighting(sightings, `t${i}`, 10 + i);
+  assert.equal(sightings.size, 500);
+  assert.equal(sightings.has("t599"), true, "the newest are kept");
+});
+
+test("warm-up countdown", () => {
+  assert.equal(getWarmupRemainingMs(null), 0);
+  assert.equal(getWarmupRemainingMs({ startedAt: 1000, durationMs: 60000 }, 31000), 30000);
+  assert.equal(getWarmupRemainingMs({ startedAt: 1000, durationMs: 60000 }, 99000), 0);
+});