How to Change the Battery in a Mains Smoke Alarm

Written by david ferguson
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How to Change the Battery in a Mains Smoke Alarm
Replace the battery in your Mains smoke alarm regularly. (fire detector on ceiling image by StarJumper from

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.

Skill level:

Things you need

  • Screwdriver
  • Replacement battery
  • Flashlight

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  1. 1

    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.

  2. 2

    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.

  3. 3

    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.

  4. 4

    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.

  5. 5

    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.

Tips and warnings

  • 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.

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