How to Replace the Battery in a Home Alarm Motion Sensor

Contact your alarm company and tell them that you plan to replace the battery in your motion sensor unit. Some units will transmit a low-battery signal to the monitoring company, which will contact you with further instructions. Skip this step if your alarm system doesn't contact anyone in the event of an alarm.

Disarm your alarm system so that it doesn't go off and possibly transmit a tampering signal to the monitoring company while you replace the battery.

Remove the cover of the motion sensor unit. Look for a tiny screw, tab or button that keeps the cover on. On some units you need to wedge a screwdriver into a tiny crevice and pop the cover off. Consult the motion sensor's manual or the manufacturer if there's no obvious way to remove the cover. Forcing the cover open may damage the unit and void your warranty.

Locate the battery and remove it. Some units have multiple batteries. You may need to unscrew the unit from the wall to find the batteries. A fingertip is sufficient to pop out most batteries. If the motion sensor uses a 9-volt battery you need to unsnap the battery's harness. Wait two minutes to let any remaining charge diminish. Otherwise any low battery signals may continue to display.

Place a new battery, or multiple batteries if necessary, in the motion sensor and re-attach the cover. Make sure the positive (+) and negative (-) ends of each battery line up correctly.

Activate your motion sensor's testing feature to ensure that the new battery is functioning properly.

Contact your alarm system's monitoring company, if applicable, to let them know you've finished replacing the battery.