Why does my smoke alarm chirp at night?

Batteries lose voltage as they cool down. At night when your home is cooler, the battery voltage drops just enough to trigger the low-battery chirp. This is why many people notice the beeping at night.

I have changed the battery but it is still beeping — why?

Some alarms have a residual charge that needs clearing. Remove the battery, press and hold the test button for 15-20 seconds to discharge, then fit the new battery. If it still chirps, the alarm may need replacing.

Can I just take the battery out to stop the beeping?

Never leave a smoke alarm without a battery. If you need to stop the noise while getting a replacement battery, remove the battery but replace it as soon as possible — ideally within hours, not days.

Low risk

Updated 30 August 2026

Smoke Detector Keeps Beeping

Your smoke detector is making an intermittent chirping or beeping sound, usually every 30-60 seconds.

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What's happening?

A chirping smoke detector is not sounding a fire alarm — it is alerting you to a fault, usually a low battery. The chirp is typically a single short beep every 30-60 seconds, very different from the continuous loud alarm of a fire detection. While not a fire emergency, it needs attention.

What usually causes it?

Low or dying battery — by far the most common cause
Battery pulled tab not fully removed on a new alarm
Detector reaching end of life (10-year sealed battery types chirp continuously)
Dust contamination on the sensor
Temperature fluctuations causing intermittent faults
Mains power failure with low backup battery (mains-wired alarms)

Is it dangerous?

The beeping itself is not dangerous, but it means the alarm may not be fully functional. A low battery could mean the alarm does not have enough power to sound properly in a real fire. Replace the battery or alarm promptly.

Can I fix it myself?

Replace the battery — use the type specified in the manual (usually a 9V PP3 or AA lithium). If the alarm has a sealed 10-year battery and is chirping, the entire unit needs replacing. For mains-wired alarms, check the backup battery compartment. After replacing the battery, press the test button to clear the fault.

When should you call an electrician?

Call an electrician if you have mains-wired alarms and the beeping continues after battery replacement, if you cannot identify which alarm is beeping, if you need a mains-wired alarm replaced, or if the alarm is at height and you cannot safely reach it.