How to change a smoke alarm battery
Quick answer: Use a stable step ladder, twist or slide the alarm off its base, swap the battery for a fresh one of the same type (usually a 9V), refit the alarm and press the test button until it sounds. If it is a sealed 10-year alarm, the whole unit is replaced, not the battery.
A smoke alarm that chirps every minute or so is telling you the battery is nearly flat. Do not take the battery out and leave it out. A working alarm is the best protection you have in a house fire.
Age UK advises testing alarms every month and changing batteries at least once a year, or fitting a sealed long-life alarm that lasts seven to ten years.
What you will need
- A step ladder
- A new battery of the right type, usually a 9V (PP3). Check the old one or the alarm label
- A soft brush or vacuum cleaner with a nozzle
- A pen to write the date on the battery
Step by step
Find out which type you have
Look at the alarm. If the label says 'sealed' or '10 year battery', you cannot change the battery: the whole alarm is replaced when it chirps. If it has a battery compartment, or you can twist it off its base, you can swap the battery.
Set up the ladder
Put the step ladder on firm, flat ground. Keep three points of contact and do not overreach. If you do not feel safe, ask someone to help or to hold the ladder.
Take the alarm off its base
Most twist anticlockwise off the base plate. Some slide off. If it is a mains alarm that is wired in, it will have a cable plug on the back. Unplug that only if you know it is safe and the circuit is off, and when in doubt leave it to an electrician.
Swap the battery
Open the battery door, take out the old battery and fit the new one the right way round. Never use a rechargeable battery unless the alarm says so.
Give the alarm a quick clean
Use a soft brush or a vacuum with a nozzle to clear dust from the vents. Dust and cobwebs can set off false alarms.
Put it back and test
Refit the alarm on the base until it clicks. Press and hold the test button until it sounds. It should be loud. If it does not sound with a new battery, replace the whole alarm.
Write the date down
Write today's date on the battery or alarm. Test it monthly. Many people change their batteries when the clocks go back or forward.
Tips
- A sealed 10-year alarm chirping means it has reached the end of its life. Replace it. The date it was made is on the label.
- Do not paint over an alarm or cover it.
- Interlinked alarms: when one sounds, they all sound. Test them all.
Stop and get help if
- The alarm is hardwired to the mains and needs replacing: this can be a like-for-like swap, but if the wiring is damaged or you are unsure, use a qualified electrician.
- It keeps going off with no cause, even with a new battery. The alarm may be faulty or too old.
- You rent: tell your landlord if an alarm is missing or broken. They have legal duties on alarms.
- You are not steady on a ladder. Ask a family member, a neighbour or a handyperson.
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Common questions
Why is my smoke alarm chirping?
Almost always the battery is low. If you have just put a new battery in and it still chirps, check the battery is fitted correctly, or the alarm has reached the end of its life.
How often should I test my smoke alarm?
At least once a month. Some fire services recommend weekly. Press the test button until it sounds.
How long do smoke alarms last?
Alarms need replacing after about ten years, even if they appear to work. Check the date on the back.
More guides
Last reviewed 17 October 2026. This guide is general information for UK homes and is not a substitute for the manufacturer's instructions. If the job involves gas, mains wiring, asbestos, structural work or working at height, or you are unsure, ask a suitably qualified person.