Short answer
A single chirp every 30 to 60 seconds from a ceiling detector is almost always a low battery. If a new battery does not stop it, or the detector is about 10 years old (check the date on the back), it is an end-of-life warning and the whole detector needs replacing. If the beep comes from the alarm keypad instead, it is a panel trouble. See keypad beeping.
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Find where the chirp is coming from
Chirps are hard to locate because high-pitched sounds bounce off walls. Stand under each detector and wait through two or three chirps. Check the ones people forget: basement stairs, inside closets, and garages. If the sound comes from the alarm keypad or touchscreen, this is a security system trouble, not the detector itself.
Low battery
- Twist the detector off its base (most turn counter-clockwise).
- Replace the battery with the type printed in the detector: commonly a 9 V, AA, or AAA. Use a brand-new battery, not one from a drawer.
- Refit it and press the test button. It should sound a full alarm.
If it keeps chirping after a new battery, take the battery out, hold the test button for about 15 to 20 seconds to drain leftover charge, then put the battery back. Hardwired detectors may need the breaker turned off during this step.
End of life
Smoke alarms are designed to be replaced 10 years after their manufacture date, which is printed on the back. CO alarms often have a shorter life, commonly 7 to 10 years depending on the model. Many detectors chirp in a distinct pattern, or show "End" on a display, when they reach end of life. Sealed 10-year lithium units cannot have their battery replaced at all; when they chirp, the whole unit is done.
Detectors connected to your alarm system
Some smoke and CO detectors are part of the security system rather than standalone alarms. Signs: a wireless smoke detector with the alarm brand's name on it, or a detector that reports a zone on the keypad. These usually report low battery to the panel too, so the keypad may show a trouble or BAT message for that zone.
- Put the account on test before removing one. Taking a system smoke detector off its base can send a tamper or trouble signal, and testing it can dispatch the fire department.
- Replace like with like. A standalone smoke alarm will not report to your monitoring company.
Do not just pull the battery
A detector with no battery cannot warn you about a fire. If you cannot replace the battery or the unit right away, get a replacement as soon as possible, and make sure other working detectors cover that area in the meantime. If a smoke or CO alarm sounds a full alarm rather than a chirp, get everyone out and call 911.