How to Change the Battery in a Wired Smoke Alarm System

Updated April 17, 2017

In the event of a fire, properly working smoke detectors provide an early warning to you and your family. Smoke detectors are typically powered by batteries or may be hard wired into a building's power system and contain a battery backup. Regardless of the type, the batteries should be replaced twice a year. If a smoke detector is occasionally beeping or chirping, it is indicating a low-battery alarm and the battery should be changed immediately.

Grasp the plastic casing of your smoke detector and gently pull it off the wall or ceiling mount. If it does not immediately disengage from the mount, it may not be a "pull off" type detector and may need to be twisted off. Do not pull the detector too far from the mount as you could possibly disconnect or damage the wiring.

Locate and remove the old battery. Detectors typically utilise a 9-volt battery housed in a battery holder. The battery is typically removed by gently prying it out of the detector, or the detector may have a small lever type tab that when pressed will "pop" out the battery. The specific battery type and removal will depend entirely on the detector model. Discard the old battery safely.

Insert a new battery into the smoke detector in the same manner as the one you removed, ensuring that the battery polarity is correct. The positive terminal of the battery must be connected to the smoke detector's positive terminal. The positive terminal of the battery and of the smoke detector will be indicated with a "+" sign. Some smoke detector models will also pictorially indicate the correct battery position. Press the test button on the detector to ensure it is operational. Grasp the plastic casing of your smoke detector and reinstall it back onto the mount.


Replace smoke detector batteries at least every six months.

Things You'll Need

  • Replacement battery
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About the Author

Jonathan Cadieux has been writing electronic and mechanical how-to articles since 2001. His work can be found online at various websites. He holds a degree in electro-mechanical engineering and has worked in the automation and electronics industry for over 20 years.