Open the sensor and locate the battery compartment

Most ADT motion sensors use a hinged plastic cover that opens from the front or side. Look for a small slot or seam where two pieces of plastic meet — this is usually where the cover releases. Gently insert a flat tool like a butter knife or flathead screwdriver into the seam and apply light pressure until the cover pops open. Do not force it, as the plastic clips can break.

Once open, you will see the battery compartment inside. ADT motion sensors typically hold one 9-volt battery, though some older models use AA or AAA batteries instead. The battery will be sitting in a plastic holder with metal contacts on either end. Note which direction the battery is facing — the positive and negative ends matter when you reinstall it.

Remove the old battery and note the orientation

Gently pull the battery out of its holder. If it is stuck, wiggle it slightly side to side rather than yanking straight up. Look at how the positive end (marked with a + symbol) and negative end (marked with a −) are positioned. Most 9-volt batteries have the terminals on top, while AA and AAA batteries have flat ends.

Before you set the old battery aside, check whether your sensor is still armed or disarmed in your ADT system. Some sensors will trigger an alert if the battery is removed while the system is armed. If you are unsure, disarm the system through your ADT panel or app before opening the sensor.

Key Takeaways

  • ADT motion sensors typically hold a single 9-volt battery, though some models use AA or AAA batteries instead.
  • Open the sensor by finding the seam in the plastic cover and gently prying it apart with a flat tool.
  • Note the battery orientation before removing it so you can reinstall the new one the same way.
  • After inserting the new battery, close the cover firmly until you hear or feel the clips lock into place.
  • The sensor should resume normal operation within a few seconds of the battery being installed.

Insert the new battery in the same direction

Take a fresh battery of the same type and voltage as the one you removed. For a 9-volt sensor, use a new 9-volt battery. For AA or AAA sensors, use the matching size. Slide the new battery into the holder, making sure the positive and negative ends align with the metal contacts inside. The battery should sit flat and snug in the holder without wobbling.

You will know the battery is seated correctly when it makes firm contact with both metal terminals. If the battery feels loose or does not sit flush, remove it and check that the holder is not bent or damaged. A poor connection will cause the sensor to malfunction or fail to communicate with your ADT system.

Close the cover and test the sensor

Press the plastic cover back onto the sensor body until you hear or feel the clips snap into place. The cover should sit flush with the rest of the sensor — if there are gaps or the cover feels loose, open it again and make sure the battery is seated properly. A loose cover can allow dust or moisture inside and damage the sensor.

After closing the cover, wait a few seconds for the sensor to power up. Most ADT motion sensors have a small LED light that blinks when the battery is installed correctly. Check your ADT panel or app to confirm the sensor is communicating with your system. If the sensor does not appear online or the LED does not light up, open the cover again and reseat the battery.

When to replace the battery

ADT motion sensors typically run on a single battery for two to three years, depending on how often the sensor triggers. Your ADT panel will usually display a low battery warning before the battery dies completely. This warning gives you time to purchase a replacement before the sensor stops working.

If your sensor stops responding to motion or disappears from your ADT app, a dead battery is often the cause. Replacing it should restore normal operation within seconds. If the sensor still does not work after you install a fresh battery, the sensor itself may be faulty and may need to be replaced through ADT.

Troubleshooting a sensor that will not turn on

If the sensor does not light up or communicate with your system after you install a new battery, first check that the battery is the correct type and voltage. A 9-volt battery will not work in an AA slot, and vice versa. Remove the battery, wait ten seconds, and reinstall it to reset the sensor.

If the sensor still does not respond, the battery holder contacts may be corroded or damaged. Look inside the compartment for any green or white buildup on the metal terminals — this is corrosion. If you see it, gently clean the contacts with a dry cloth or a pencil eraser. Reinstall the battery and test again. If the sensor remains unresponsive, contact ADT to discuss replacement options.

Frequently Asked Questions

What type of battery does my ADT motion sensor use?

Most modern ADT motion sensors use a single 9-volt battery. Older models may use AA or AAA batteries instead. Check the label inside the battery compartment or your sensor's manual to confirm the correct type before purchasing a replacement.

Will replacing the battery trigger an alarm?

Replacing the battery should not trigger an alarm if your system is disarmed. If your system is armed when you open the sensor, some models may send an alert to your ADT monitoring center. Disarm your system through your panel or app before opening the sensor to avoid an unnecessary dispatch.

How long does a motion sensor battery last?

A typical ADT motion sensor battery lasts two to three years under normal use. Sensors that trigger frequently will drain the battery faster. Your ADT panel will display a low battery warning when the battery is running low, usually giving you several weeks to replace it before it dies.

Can I use a rechargeable battery in my motion sensor?

Rechargeable batteries are not recommended for ADT motion sensors. They have a lower voltage than standard alkaline batteries and may not provide enough power for the sensor to function properly. Use a fresh alkaline battery of the correct type for best results.

What should I do if the sensor still does not work after I replace the battery?

First, remove the battery, wait ten seconds, and reinstall it to reset the sensor. Check that the battery is the correct type and fully inserted. If the sensor still does not respond, the battery holder contacts may be corroded — clean them gently with a dry cloth. If it remains unresponsive, the sensor may need to be replaced through ADT.