Replace the battery by opening the sensor cover, removing the old battery, and inserting a new one of the same type

ADT motion sensors run on replaceable batteries that typically last one to three years depending on how often the sensor triggers. When the battery dies, the sensor stops reporting motion to your system, and ADT usually sends you a low-battery alert through your app or panel before that happens. You do not need a technician — the replacement takes about two minutes and costs between $5 and $15 for a new battery.

The exact steps depend on your sensor model, but the process is nearly identical across ADT's residential line. Most sensors use either a 9-volt battery or two AA batteries. Check your sensor's label or your system paperwork to confirm which type yours needs before you buy a replacement.

Key Takeaways

  • ADT motion sensors use either 9-volt or AA batteries, and you must match the type your sensor requires.
  • The sensor cover usually twists or slides off without tools, and the battery compartment is clearly marked inside.
  • After you insert the new battery, the sensor should show a green light or send a signal to your panel within 30 seconds.
  • If the sensor does not respond after a battery change, remove and reinsert the battery to reset the connection.
  • Keep spare batteries on hand because motion sensors often fail without warning, and a dead sensor leaves a gap in your coverage.

Locate the battery compartment on your sensor

ADT motion sensors are small white or black boxes, usually mounted on a wall or corner at least six feet high. The battery compartment is on the back or bottom of the unit. Look for a small seam or a label that says "Battery" — this marks where the cover opens.

Some models have a cover that twists counterclockwise; others slide straight out. explore gentle pressure and turn or pull slowly. Do not force it, because the plastic can crack. If the cover does not budge after light pressure, check whether there is a small screw holding it in place — a few older ADT models use one, and you will need a Phillips screwdriver to remove it.

Remove the old battery and note its type

Once the cover is open, you will see the battery sitting in a plastic holder or metal contacts. The battery type is printed on its side — look for "9V" or "AA" and note the brand if you can. Take a photo with your phone if you want to match it exactly when you shop.

Gently lift or slide the old battery out of its holder. If it is stuck, do not pry it with a metal tool — use your fingernail or a plastic spoon to avoid damaging the contacts inside. Dispose of the old battery according to your local rules; many retailers like Best Buy and Home Depot take used batteries for free.

Insert the new battery and close the cover

Buy a fresh battery of the same type — a 9-volt Duracell or Energizer, or two AA batteries if your sensor uses that format. Insert the new battery into the holder, making sure the positive and negative ends align with the metal contacts. The battery should sit flat and click or snap into place.

Close the cover by twisting it clockwise or sliding it back in, depending on your model. You should hear or feel a small click when it seats properly. Do not overtighten a twist cover — snug is enough.

Confirm the sensor is working

After you close the cover, the sensor should send a signal to your ADT panel within 30 seconds. Check your panel or app for a green light or a status message that says the sensor is online. If you see a low-battery warning still showing, wait another minute — sometimes the panel takes a moment to update.

If the sensor does not show as active after two minutes, open the cover again and remove the battery for 10 seconds, then reinsert it. This resets the sensor's connection to your panel. Close the cover and wait another 30 seconds. If it still does not respond, the battery may be defective — try a different brand or a battery from a different package.

Know when to replace the battery before it dies

ADT sends a low-battery alert to your panel and app when the battery is running low, usually one to two weeks before it fails completely. When you see that alert, replace the battery within the next few days. Do not wait until the sensor goes offline, because a dead sensor leaves a blind spot in your motion coverage.

If you ignore the alert and the sensor dies, your system will show it as offline or "not responding" on your panel. You will still have coverage from your other sensors, but that zone is unprotected until you replace the battery. Some ADT plans charge a service fee if a technician has to come out to replace a battery, so doing it yourself saves money.

Troubleshoot a sensor that does not respond after battery replacement

A sensor that stays offline after a new battery usually has one of three problems: the battery is installed backwards, the battery is defective, or the sensor itself has failed. Start by opening the cover and checking that the positive end of the battery (marked with a + sign) faces the correct direction — your sensor's manual or the inside of the cover usually shows which way it should go.

If the direction is correct, remove the battery, wait 30 seconds, and reinsert it. If the sensor still does not respond, try a battery from a different package or brand — sometimes a single battery is dead on arrival. If a fresh battery from a different source does not work, the sensor may have a hardware failure, and you will need to contact ADT to have it replaced under your service plan.

Frequently Asked Questions

How do I know what type of battery my ADT motion sensor uses?

Check the label on the back or bottom of the sensor — it usually lists the battery type. You can also look at your system paperwork or the original installation guide. If you cannot find either, contact ADT with your sensor model number and they will tell you which battery to buy.

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 last as long between charges. Stick with alkaline batteries like Duracell or Energizer for the longest battery life and most reliable performance.

What if my sensor shows low battery but the battery is brand new?

A new battery that shows low usually means the battery is defective or was installed backwards. Remove it, check that the positive end faces the correct direction, and reinsert it. If the alert persists, try a battery from a different package. If a second battery shows the same warning, the sensor itself may be failing and you should contact ADT.

Do I need to disarm my system before replacing the battery?

No, you can replace the battery while your system is armed or disarmed. The sensor will go offline briefly while the cover is open, but your other sensors will continue to work. If you want to avoid any alerts, disarm the system first, but it is not required.

How often should I replace the battery in my motion sensor?

Most ADT motion sensors run for one to three years on a single battery, depending on how often they trigger. You will get a low-battery alert when it is time to replace it — you do not need to replace it on a schedule. Keep spare batteries on hand so you can replace them as soon as the alert appears.