Open the sensor and locate the battery compartment

ADT motion sensors hold their battery in a compartment on the back or side of the unit. To reach it, you need to open the sensor casing first. Most ADT motion sensors have a small slot or seam running around the edge — this is where the two halves separate.

Look for a thin plastic tab or notch along that seam. Insert a flat tool (a butter knife, flathead screwdriver, or even a credit card) gently into the slot and explore steady pressure. The casing will pop apart. Do not force it — if it resists, you are likely in the wrong spot. Once open, you will see the battery sitting in a plastic holder, usually marked with a plus and minus sign showing which direction it goes.

Write down the battery type before you remove the old one. Most ADT motion sensors use a 9-volt battery or AA/AAA batteries, but the label on the compartment will tell you exactly which one your model needs. Take a photo of the label with your phone if you are unsure.

Key Takeaways

  • ADT motion sensors open by gently prying the seam with a flat tool until the two halves separate.
  • The battery compartment is clearly labeled with the battery type and polarity (plus and minus).
  • Most ADT sensors use either a 9-volt battery or AA/AAA batteries — check your specific model's label.
  • After inserting the new battery, close the casing firmly until you hear or feel a click, then test the sensor by walking past it.

Remove the old battery and insert the new one

Lift the old battery straight out of its holder. If it is stuck, do not pry at it with metal tools — use your fingernail or a plastic spoon to avoid damaging the compartment. Once removed, check the expiration date on the new battery to confirm it has not sat on a shelf for years.

Insert the new battery into the holder with the correct polarity. The positive terminal (marked with a plus sign) must face the direction shown in the compartment. If you insert it backward, the sensor will not work, but it will not damage anything — you will straightforward need to flip it. Push the battery down firmly until it sits flat in the holder.

Close the casing and test the sensor

Align the two halves of the casing so the seam matches up evenly. Press down firmly along the entire edge until you feel or hear a click. The casing should sit flush with no gaps. If there are gaps, the sensor may not seal properly and moisture could enter.

Once closed, test the sensor by walking past it from about six feet away. Most ADT motion sensors have a small LED light on the front that blinks when motion is detected. If the light blinks as you move, the battery is working and the sensor is communicating with your system. If nothing happens, open the casing again and check that the battery is inserted with the correct polarity.

What to do if the sensor still does not respond

If the sensor does not blink or respond after you have replaced the battery and tested it, the problem is usually one of three things: the battery is inserted backward, the casing is not fully closed, or the sensor itself has failed.

Start by opening the casing again and flipping the battery 180 degrees. Close it and test. If that does not work, open it once more and make sure the battery is making firm contact with both terminals in the holder — sometimes a battery can sit slightly loose. If the sensor still does not respond after these steps, the motion sensor may need to be replaced. Contact ADT support with your system model number and they can send a replacement or walk you through additional troubleshooting.

When to replace the battery before it dies

ADT motion sensors usually alert you when the battery is running low. Your system panel or mobile app will show a low-battery warning for that specific sensor. When you see this message, you have roughly one to two weeks before the battery fully drains, so replace it within that window.

Do not wait until the sensor stops working entirely. A dead battery means the sensor cannot detect motion, and your system will show it as offline. This creates a gap in your coverage. Most ADT batteries last one to three years depending on how often the sensor detects motion, so if you have not replaced one in over a year, check your system for any low-battery alerts.

Frequently Asked Questions

Can I use a rechargeable battery in my ADT motion sensor?

Rechargeable batteries work in most ADT motion sensors, but they discharge faster than standard alkaline batteries. If you use them, you may see low-battery warnings more frequently. Standard alkaline batteries are more reliable for motion sensors because they hold their charge longer during periods of low activity.

What if I cannot get the casing open?

If the seam is too tight, try running a thin plastic tool (like a credit card or old gift card) along the seam first to loosen it, then use a flat screwdriver. Avoid metal tools that could scratch the plastic or slip and damage the sensor. If it still will not open, contact ADT — forcing it may crack the casing.

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

No, you do not need to disarm your system. Replacing the battery is a routine maintenance task. However, while the sensor is open and the battery is out, it will not detect motion. If you are concerned about coverage, you can disarm the system temporarily while you work.

How do I know which battery type my sensor uses?

Open the battery compartment and look at the label inside. It will clearly state the battery type — usually 9V, AA, or AAA. If the label is worn or unreadable, check your ADT system documentation or contact ADT support with your sensor model number.

Will replacing the battery reset my sensor settings?

No. Replacing the battery does not erase any settings or require you to re-pair the sensor with your system. The sensor will resume working exactly as it was configured once the new battery is installed and the casing is closed.