Which smoke detector is beeping?
Stop guessing. Your phone measures the chirp in each room and names the loudest detector.
Free · No app or sign-up
· Nothing leaves your phone
Non-stop beeping, or Kidde's CO pattern — four beeps, pause, repeat?[4] That's an alarm, not a chirp. Get everyone outside, then call 911. What to do now →
How it works
Pick your rooms
Tap each room that has a smoke or carbon monoxide detector.
Stand under each one
Your phone listens, then moves to the next room on its own.
Get the answer
The room with the loudest chirp is your culprit.
What do smoke detector chirp patterns mean?
Counting chirps will not tell you a low battery from an alarm at the end of its life. What actually separates them is whether the alarm has a battery you can remove, and how old it is.
Every documented pattern, with sources| 1 chirp every 30–60 seconds | Kidde documents this as a low battery — or, on a sealed alarm with no battery door, the alarm itself is finished.[1] |
|---|---|
| 3 chirps a minute | First Alert documents this as a malfunction. A fresh battery will not clear it.[2] |
| 5 chirps a minute | Low battery or end of life — First Alert uses one pattern for both, so this alone does not tell you which.[3] |
| Continuous | Real alarm. Check for smoke or CO now. |
The last row is ours rather than a manufacturer's: whatever the brand, a continuous alarm is treated as real until you have checked.
Why are smoke and CO detector chirps so hard to find?
A chirp is short and high-pitched, and it bounces off walls, ceilings, anything hard — so your ears can't tell where it came from. That's why you're standing in the hallway at 2 AM tilting your head.
WhichBeep listens between 2,500–4,500 Hz — our own detection setting rather than a published detector specification — and measures loudness at each detector instead of asking your ears to pick a direction.
Sources
Every beep pattern on this page comes from the manufacturer's own documentation. Where a manual contradicted us, we changed the page.
- [1] Kidde. What Causes Consistent Chirping? (retrieved 2026-09-07)
- [2] First Alert. User's Manual: Wireless Interconnect Smoke Alarm, Model SA511 (M08-0194-005) (retrieved 2026-09-06)
- [3] First Alert. User's Manual: Smoke Alarm, AC Powered with Strobe Light and 10-Year Sealed Battery Backup, Model SM110LED-AC (retrieved 2026-09-06)
- [4] Kidde. Why Is My Carbon Monoxide Alarm Beeping or Chirping? (retrieved 2026-10-02)