Guide
Smoke alarm beeping? Why it chirps and how to stop it
A single chirp every minute or so is almost always a low battery, and on a mains alarm it is the backup cell. If a fresh battery does not stop it, the alarm itself has usually reached the end of its life, which for most is ten years from manufacture.
Chirp, beep or full alarm: which one you have
A smoke alarm has two voices. The full alarm is loud, continuous and impossible to sleep through. The chirp is a single short note repeated at intervals, often every thirty to sixty seconds, and it is the alarm telling you about itself rather than about a fire. Before doing anything, stand under each device and make sure the noise is coming from the smoke alarm and not from a carbon monoxide alarm, an intruder alarm panel or a forgotten gadget in a drawer.
| What you hear | Usual cause | First thing to try |
|---|---|---|
| One chirp every minute or so | Low battery | Replace the battery, or the whole unit if it is sealed |
| Chirping carries on with a new battery | Battery not seated, or the alarm is at end of life | Reseat it, then check the date on the back |
| Full alarm with no smoke | Steam, cooking fumes, dust or insects | Pause it with the test button and clean it |
| Every alarm in the house sounds at once | Interlinked set, one device triggered | Find the one that started it, then deal with that one |
Why it always starts at night
It is not bad luck. Battery voltage falls as the temperature drops, and the coolest part of the night is when a cell that was just about coping in the day crosses the low battery threshold. Fire and rescue services point to exactly this. The practical upshot is that a 3am chirp is a real warning, not a glitch that will clear itself by breakfast.
On many alarms a press of the test button silences the low battery chirp for a while, and the alarm still detects smoke during that time. Devon and Somerset Fire and Rescue's advice is to replace the battery within seven days, because after that the alarm may not have enough power left to warn you of a real fire.
Stopping the chirp, alarm by alarm
What to do depends on how the alarm is powered, which is usually printed on the back or obvious from whether it has a wire going into the ceiling.
- Replaceable battery alarm. Fit a new battery of the type printed on the alarm, close the cover fully and press the test button. Most alarms will not close properly on a battery that is not seated.
- Ten year sealed battery alarm. The battery is sealed in for the life of the alarm. A low battery chirp means the whole alarm is due for replacement.
- Mains alarm with a backup battery. These chirp when the backup cell is low, exactly as a battery alarm does. Switch off the circuit that feeds it at the consumer unit, twist the head off its base, change the cell and refit it. Some models also need the test button held for a few seconds to clear a stored warning, and the manual says which.
Taking the battery out and leaving it out is the one response that is never right. An alarm with no power gives no warning.
False alarms when there is no fire
Smoke alarms react to things that are not smoke: steam drifting out of a bathroom, fumes from a grill, toast, candles, dust from sanding and the occasional insect inside the sensing chamber. The test button pauses most alarms, and they return to full sensitivity on their own after about ten minutes.
If one alarm keeps going off, look at where it is. An alarm next to the kitchen door or the bathroom will keep doing this however often it is cleaned, and the answer is to move it or swap it for a heat alarm in the kitchen, which responds to a rise in temperature rather than to particles. A gentle vacuum around the vents with a brush attachment clears dust and insects.
When it is the alarm and not the battery
Alarms carry a replace by date or a manufacture date on the back, and the usual life is ten years. A house fitted out in one go reaches that date in one go, which is why a single chirping alarm is often the first of several. Fire service advice is to test every alarm monthly by holding the test button until it sounds, which checks the sensor and the power together.
Replacing alarms at the end of their life on existing wiring is £120 to £280 for a typical house. A new set of three interlinked mains alarms is £300 to £600, and a radio interlinked sealed battery set of the same size £180 to £400. Swapping a mains alarm like for like is not notifiable work in England. A new dedicated circuit for the alarms is, and comes with a certificate.
Rented homes, and the rules in Scotland
In England, private landlords have had to provide at least one smoke alarm on every storey with a room used as living accommodation, and a carbon monoxide alarm in any such room with a fixed combustion appliance other than a gas cooker, since 1 October 2022. The alarms must be working on the day a new tenancy begins, and the landlord must repair or replace one once told it is faulty. The council can fine a landlord up to £5,000 for failing to comply with a remedial notice.
A tenant with a chirping alarm should report it in writing rather than pull the battery. In Scotland the standard is wider and covers owner occupiers too: interlinked alarms in the room used most during the day and in every hall and landing, and a heat alarm in the kitchen.
Common questions
Why is my smoke alarm still beeping after I changed the battery?
The battery may not be seated, the cover may not be fully closed, or a mains alarm may need its test button held to clear the warning. If none of that works, check the date on the back: an alarm near ten years old is telling you it needs replacing.
How do I find which interlinked alarm went off?
Many interlinked alarms show a different light pattern on the one that started it, and the manual describes it. Silence the set, then look at each unit in turn before resetting.
Can I fit a mains smoke alarm myself?
Replacing a mains alarm like for like on the same base is within reach for a competent person with the circuit isolated. Running a new circuit for alarms is notifiable in England and Wales, so it needs a registered electrician or a building control application.
How often should smoke alarms be tested?
At least once a month, by holding the test button until the alarm sounds. Fire and rescue services recommend the same routine for every type of alarm.