How to Change the Battery in a Mains Smoke Alarm

Updated April 17, 2017

Mains smoke alarms are an essential home safety device, saving countless lives worldwide every year. Alerting you to house fires quickly, mains alarms are often supported by a backup battery to guard against power failures. Changing the battery on a regular basis keeps your alarm functioning at its optimum, to make sure your family is protected against the threat of domestic fires.

Turn off the Mains power before touching the alarm or its casing. Mains alarms contain live electricity and can pose a shock risk unless the power is switched off. The Mains power switch will be accessible near your central fuse box, usually by the front door or in the basement, and you should flick the switch into the 'off' position to turn off the alarms.

Remove the casing from the front of the alarm, using the flashlight to aid visibility. This generally screws off, although some units require a push and unscrew motion.

Remove the used battery from the alarm, leveraging the end of the battery out first before disconnecting the pins. Dispose at your local battery recycling facility for safe, environmentally-friendly disposal.

Insert the replacement battery, taking care to fit it the correct way round. Be sure that the positive and negative pins correctly correspond with the fitting in the alarm.

Replace the alarm casing and turn the Mains power back on at the fuse box. Be sure to screw the alarm casing tightly back into place.


Change the battery in your Mains smoke alarm at least once a year. Keeping the battery up to date is an essential safety backup and it's better to consistently replace your battery for greater peace for mind.


Make sure your battery is working by testing the alarm with the mains power off. Light a match and blow it out directly underneath the alarm to determine whether the battery has been correctly installed.

Things You'll Need

  • Screwdriver
  • Replacement battery
  • Flashlight
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About the Author

David Ferguson has been a freelance Web writer since 2005, writing for various online media, including a feature in "Personal Branding Magazine" in 2008. Ferguson qualified with an English language and English literature joint master's degree from the University of Glasgow.