How to Replace a Battery in an ADT Door Sensor

Close the door guarded by the sensor in which you intend to replace the battery.

Switch the alarm system to the "test" mode by entering the user access code, followed by the number 5 and finally the number 0.

Pry the cover from the sensor requiring the battery change. Use your finger to disengage the finger latch or pry the cover free from the sensor using a flat screwdriver, depending on your type of sensor.

Pry the battery from the slot to the right of the inside of the sensor with a flat screwdriver. Slide the blade of the screwdriver into the bottom of the battery, the negative polarity side, for easiest removal.

Wait 30 seconds after removing the spent battery before installing the new battery.

Place the new 3-volt Lithium battery into the battery slot inside the door sensor. Align the polarity of the battery according to the "+" and "-" symbols on the sensor.

Replace the cover onto the sensor by aligning one side first, and then press firmly to snap the other side back into place.

Open and close the door assigned to the sensor. Listen for three beeps from the control panel to confirm connection between the sensor and the touchpad.

Arm the alarm and disable the "test" mode by entering your user number and the number 1 using the touchpad. Repeat your entry of the user number followed by the number 1 to end the battery change process.