Customer FAQs Discover answers to the most frequently asked questions from ADT customers with the click of a button. 1. How do I replace a door/window sensor battery? When the battery in your door/window contact needs to be replaced, a “zone trouble” indicator will appear on your alarm keypad and/or “sensor trouble” indicator will appear on your ADT Pulse device. You should replace the battery as soon as these indicators appear. A door and window contact requires (1) CR123 3 volt battery (in some systems, the door and window contact will be a very slim device and will contain a single, CR2032 battery). This battery can often be purchased at your local hardware, mass retailer or battery store. Before you replace the battery, put your system into test mode to prevent false alarms. Log into MyADT.com and select My Alarm from the dashboard.Once you click My Alarm, a menu will appear.From the menu, select System Management. Select Place System On Test. (Note: You can also call 800-ADT-ASAP to put your system into test mode.) To change the battery, use a flathead screwdriver to push in the tab on the end of the contact. An arrow on the front of the contact points to where the tab is located. Replace the battery, observing the proper polarity. Then, replace the front cover by snapping it into place. The security system may need to be reset by entering your code into your system and hitting off twice. Remember to remove the system from Test Mode.Go to MyADT.com and click on My Alarm from the System Management option, select Stop Test to remove the system from test mode and restore operations. Watch this video for step-by-step instructions.