Which detector is chirping?
100% free. We'll use your phone's mic to find which detector needs a new battery.
No app to download. 3 steps. Under 5 minutes.
How it works
Can't tell which smoke detector or carbon monoxide detector is beeping? WhichBeep uses your phone's microphone to measure the chirp volume at each detector in your home — whether it's a smoke alarm, CO alarm, or combo unit — then compares the readings to tell you exactly which one needs attention.
- 1Name your detector locations — bedroom, hallway, kitchen, etc.
- 2Walk to each detector — hold your phone near it and wait for the chirp.
- 3Get your answer — we'll rank every location by chirp volume and tell you the culprit.
The whole process takes under 5 minutes. No app to download, no account to create, and no audio data ever leaves your phone.
Why are smoke and CO detector chirps so hard to find?
If you're searching for "which smoke detector is beeping" or "carbon monoxide detector chirping" at 2 AM, you're not alone. Both smoke detectors and CO detectors use the same type of chirp to signal low battery — a short, high-pitched beep in the 2,500–4,500 Hz range. At that frequency, sound bounces off walls, ceilings, and hard surfaces. Your ears genuinely cannot determine the direction.
This is why people end up wandering their homes at night, tilting their heads, trying to figure out which smoke detector is chirping. The most common advice online is to "just replace all the batteries" — which works, but isn't helpful when you have 5+ detectors and it's the middle of the night. WhichBeep solves this by measuring the actual chirp volume at each location, giving you a definitive answer in minutes.
What do the chirp patterns mean?
- Single chirp every 30–60 seconds — Low battery. This is the most common reason for a beeping smoke detector. Replace the battery and the chirping will stop.
- Three chirps in a row — End-of-life warning on some models. The entire detector unit needs to be replaced.
- Five chirps — Sealed-unit end-of-life. These detectors have a built-in 10-year battery that cannot be replaced. You need a new detector.
- Continuous beeping — This is an active alarm, not a low battery. Check for smoke, carbon monoxide, or other hazards immediately.
Carbon monoxide detector chirps
CO detectors chirp for the same reasons as smoke detectors — low battery or end-of-life. If your carbon monoxide detector is beeping every 30–60 seconds, it almost certainly needs a new battery. The chirp sounds nearly identical to a smoke detector chirp, which is why it's so hard to tell them apart when you have both types in your home.
Important: A CO detector that beeps 4 times in a row, pauses, then repeats is signaling a carbon monoxide emergency — not a low battery. Open windows, get everyone outside, and call 911. WhichBeep is designed for the low-battery chirp, not active CO alarms.
Smoke detector battery types
Once you've found the beeping detector, you'll need the right battery. Most smoke detectors use a 9V battery (the rectangular one), though newer models may use AA or CR123A lithium batteries. Check the label on your detector or open the battery compartment to confirm the type before purchasing a replacement.