Open the sensor and locate the battery compartment

ADT motion sensors have a removable cover that slides or pops off the front or back of the unit. Look for a small slot or seam running along one edge — this is where the cover releases. Gently pry the edge with your fingernail or a plastic tool (not a metal screwdriver, which can scratch the housing). The cover will slide out or pop free, revealing the battery compartment inside.

Once the cover is off, you will see a battery sitting in a plastic holder or clip. Most ADT motion sensors use a 9-volt battery or two AA batteries, depending on the model. The battery will have a label or marking showing which direction it goes — usually a plus and minus sign printed on the compartment itself.

Remove the old battery and note its orientation

Before you pull the old battery out, take a photo or write down which way the positive and negative ends are facing. This matters because putting the battery in backwards will prevent the sensor from working. Gently lift or slide the battery out of its holder — it may be held in place by a spring clip, so explore steady pressure rather than jerking it.

If the battery is stuck, do not force it. A battery that has been in place for years can corrode slightly. Try rocking it gently side to side, or use a plastic spoon handle to explore even pressure. Once it comes free, set it aside.

Insert the new battery in the correct direction

Take your replacement battery — a fresh 9V or AA, depending on what your sensor uses — and align it with the markings in the compartment. The positive end (marked with a plus sign) should face the direction shown on the label. Slide or press the battery into the holder until you hear or feel it click into place. The spring clip should hold it firmly without requiring excessive force.

If your sensor uses two AA batteries, insert them one at a time, making sure each one is oriented correctly. Some sensors have the batteries stacked end-to-end, while others sit side by side. Follow the diagram printed inside the compartment.

Close the cover and test the sensor

Slide the cover back onto the sensor body until it clicks or seats fully. The cover should sit flush with no gaps. If it does not close smoothly, the battery may not be seated correctly — pop the cover back off and reseat the battery.

Most ADT motion sensors have a small LED light on the front that blinks when the battery is good and the sensor is armed. If the light does not appear after you close the cover, wait 10 to 15 seconds — some sensors take a moment to power up. If the light still does not appear, open the cover again and check that the battery is making full contact with the metal terminals in the holder.

Know when your sensor battery is running low

ADT motion sensors send a low-battery signal to your control panel when the battery voltage drops below a certain threshold. You will see a low-battery alert on your keypad or receive a notification through the ADT mobile app. This usually happens weeks or months before the battery is completely dead, giving you time to replace it without losing protection.

If you ignore the low-battery alert, the sensor will eventually stop reporting motion to your system. Your ADT monitoring service may also flag the sensor as offline. Replace the battery as soon as you see the alert to keep the sensor active.

Choose the right replacement battery type

ADT motion sensors use either 9-volt alkaline batteries or AA alkaline batteries. Check the label on your sensor or the battery compartment to see which one yours requires. You can buy these at any grocery store, pharmacy, or hardware store — they are standard sizes and cost between two and five dollars each.

Alkaline batteries last longer than carbon-zinc batteries in motion sensors, so choose alkaline if you have a choice. Some people use rechargeable batteries, but motion sensors draw power intermittently and in small amounts, so rechargeable batteries may not last as long between charges. Stick with alkaline unless your sensor specifically says rechargeable batteries are safe.

Key Takeaways

  • ADT motion sensors have a sliding or pop-off cover that reveals the battery compartment inside.
  • Most ADT sensors use either a single 9-volt battery or two AA batteries, and the battery must be inserted with the correct polarity or the sensor will not work.
  • Your ADT control panel will alert you when the battery is running low, usually weeks before it dies completely.
  • Replacement batteries are standard alkaline types available at any store, and you should replace them as soon as you see a low-battery alert to keep your sensor armed.

Frequently Asked Questions

How often do I need to replace the battery in my motion sensor?

Alkaline batteries in motion sensors typically last one to three years, depending on how often the sensor detects motion. A sensor in a hallway you walk through daily will drain the battery faster than one in a rarely-used room. Your ADT system will alert you when the battery is low, so you do not have to guess.

What if my sensor still does not work after I put in a new battery?

First, make sure the battery is inserted the correct way — check that the positive end matches the plus sign in the compartment. If it is oriented correctly and the sensor still does not respond, try a different new battery to rule out a defective one. If a second battery does not work, the sensor itself may be faulty and you should contact ADT.

Can I use rechargeable batteries in my ADT motion sensor?

Rechargeable batteries work in most ADT sensors, but they may not last as long as alkaline batteries because motion sensors draw power in small, irregular bursts. If you want to use rechargeable batteries, choose ones rated for low-drain devices and check your sensor manual to confirm they are safe.

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

You do not have to disarm the system, but it is a good idea to avoid false alarms. If you disarm the system before opening the sensor, the motion detector will not trigger while the cover is off. If you leave the system armed, the sensor may send a signal when you open it.

Where can I buy replacement batteries for my ADT sensor?

Standard 9-volt and AA alkaline batteries are sold at grocery stores, pharmacies, hardware stores, and online retailers. You do not need to buy them from ADT — any brand of alkaline battery in the correct size will work in your sensor.