diff --git a/__tests__/alarmSocket.test.ts b/__tests__/alarmSocket.test.ts
index 65113be..72f1dee 100644
--- a/__tests__/alarmSocket.test.ts
+++ b/__tests__/alarmSocket.test.ts
@@ -88,7 +88,6 @@ describe('frame contract', () => {
       action: 'trigger',
       message: 'Fire drill',
       serverTime: '2026-10-18T17:00:00Z',
-      autoStopSeconds: 60,
     });
     expect(parseFrame(raw)).toEqual({
       type: 'alarm',
@@ -97,10 +96,25 @@ describe('frame contract', () => {
       action: 'trigger',
       message: 'Fire drill',
       serverTime: '2026-10-18T17:00:00Z',
-      autoStopSeconds: 60,
     });
   });
 
+  it('ignores a legacy autoStopSeconds field instead of carrying it forward', () => {
+    // The service no longer sends it; a stale sender must not resurrect the
+    // "alarm expires on a timer" behaviour in any consumer.
+    const frame = parseFrame(
+      JSON.stringify({
+        type: 'alarm',
+        alertId: 'a',
+        eventId: 'e',
+        action: 'trigger',
+        autoStopSeconds: 60,
+      }),
+    );
+    expect(frame.type).toBe('alarm');
+    expect(frame).not.toHaveProperty('autoStopSeconds');
+  });
+
   it('parses a disarm frame', () => {
     const frame = parseFrame(
       JSON.stringify({ type: 'alarm', alertId: 'a', eventId: 'e', action: 'disarm' }),