Open the sensor cover and remove the old battery

ADT motion sensors run on a single AA or AAA battery depending on your model. To replace it, first locate the small slot or seam on the front or side of the sensor — this is where the cover opens. Use a flat tool like a butter knife or flathead screwdriver to gently pry the cover away from the body. Do not force it; the cover should slide or pop off with light pressure.

Once the cover is open, you will see the battery sitting in a plastic holder. Note which direction the battery is facing — the positive end (marked with a + sign) should be pointing toward the spring contact. Slide the battery out of its holder. If it is stuck, gently wiggle it side to side rather than pulling straight out.

Install the new battery in the correct direction

Take a fresh AA or AAA battery — check your sensor's manual or the battery compartment itself to confirm which size you need. Slide the new battery into the holder with the positive end facing the same direction as the old one was. You should hear or feel a small click as the battery seats into place and makes contact with the spring.

Do not force the battery in. If it does not slide smoothly, remove it and check that you are inserting it in the correct direction. The battery should sit flat and flush with the holder. Forcing a battery in the wrong direction can damage the spring contact and prevent the sensor from working even with a fresh battery installed later.

Close the cover and test the sensor when ready

Slide or snap the cover back onto the sensor body until it sits flush. You may hear a small click as it locks into place. Most ADT sensors have a test button on the cover — press and hold it for three seconds. Your sensor should emit a beep or flash a light to confirm it is working and the battery is making proper contact.

If nothing happens, open the cover again and check that the battery is fully seated in its holder. Make sure the positive end is facing the spring contact. Close the cover and test again. If the sensor still does not respond, try a different new battery — occasionally a battery from the store is defective or partially drained before you use it.

Recognize low-battery alerts from your control panel

ADT motion sensors send a low-battery signal to your control panel before the battery dies completely. You will see a low-battery alert on your keypad or in the ADT mobile app — usually a message that says "Low Battery" followed by the sensor's zone number or name. This alert gives you time to replace the battery before the sensor stops working.

Do not ignore this alert. A sensor without battery power cannot detect motion, which means your system will not trigger an alarm if someone enters that room. Replace the battery within a few days of seeing the alert to keep that zone protected. The alert will clear automatically once you install a fresh battery and the sensor confirms it has power.

Troubleshoot when a sensor stops responding after battery replacement

If you have replaced the battery, closed the cover, and the sensor still will not beep or light up during the test, the problem is usually one of three things. First, the battery may be inserted backward — open the cover and flip it so the positive end faces the spring contact. Second, the battery itself may be defective — try a different new battery from a different package or brand.

Third, the sensor may have a faulty spring contact or internal circuit. If you have tried two different fresh batteries in the correct direction and the sensor still does not respond, contact ADT to report the sensor as faulty. They can send a replacement or troubleshoot further over the phone. Do not assume the sensor is broken until you have tested it with at least two different batteries.

Key Takeaways

  • ADT motion sensors use a single AA or AAA battery; check your manual or the compartment label to confirm which size your model needs.
  • Pry the cover open gently with a flat tool, note the direction the old battery faces, and insert the new battery the same way with the positive end toward the spring.
  • Press the test button after closing the cover to confirm the sensor is working and the battery is making contact.
  • Your control panel will alert you to a low battery before it dies, giving you time to replace it before the sensor stops protecting that zone.
  • If a sensor does not beep after battery replacement, try a different new battery in the correct direction before contacting ADT about a faulty sensor.

Frequently Asked Questions

What type of battery does my ADT motion sensor use?

Most ADT motion sensors use either an AA or AAA battery. The easiest way to find out is to open the sensor cover and look at the battery compartment — it will be shaped to fit only one size. You can also check your original paperwork or the ADT website by entering your sensor model number.

How often do I need to replace the battery?

A fresh battery typically lasts one to three years depending on how often the sensor detects motion. Sensors in high-traffic areas drain batteries faster than sensors in rarely-used rooms. Your control panel will alert you when the battery is low, so you do not have to guess or replace batteries on a schedule.

Can I use a rechargeable battery in my motion sensor?

Rechargeable batteries work in most ADT sensors, but they drain faster than alkaline batteries and may not trigger the low-battery alert reliably. Stick with standard alkaline AA or AAA batteries for the most consistent performance and earliest warning when replacement is needed.

What if my sensor does not beep after I replace the battery?

Open the cover again and confirm the battery is fully seated in its holder and facing the correct direction with the positive end toward the spring. If it is, try a different new battery — the first one may be defective. If a second battery also does not work, the sensor itself may be faulty and you should contact ADT for a replacement.

Do I need to tell ADT that I replaced the battery?

No. Replacing the battery is a normal maintenance task you can do yourself. You only need to contact ADT if the sensor stops working after you replace the battery, or if the low-battery alert does not clear after you install a fresh one.