ADT Door/Window Sensor will not complete setup or pairing

The checks in more detail

Then enrol it: put the panel into sensor or zone programming mode, which needs the installer or master code, and trigger the sensor by opening the case or pulling the battery tab, so it sends its enrolment signal. The panel beeps and shows the zone. Name the zone and set its type, such as entry and exit or perimeter, according to how it should behave. After enrolment, test the sensor in the panel's test mode: open and close the door and check that the panel reports each event. If the sensor reports open when the door is closed, the gap is too wide or the parts are misaligned.

If it does not enrol, check the battery's orientation, the distance to the panel and that the panel has a free zone. Keep the sensor within range of the panel, ideally within a few meters and without large metal objects between. Tell the monitoring company about new zones, so that they hold the correct list. Record the zone numbers and locations on a sheet near the panel. Check batteries yearly. Remember that a door and window sensor detects opening and not breaking glass, so combine it with other sensors where needed. If you add many sensors, plan the zone list so that entry doors have the right delays.

Plan the zone list before you fit several sensors. Entry doors need a delay so you can reach the keypad, interior doors may need to be bypassed when you are home, and ground-floor windows are perimeter zones that should trigger at once. Setting the zone type correctly at enrolment saves a call later. Also check that the frame is not warped or painted over, since a door that does not close fully leaves the magnet outside its working distance, and the sensor then reports open even though the door looks shut. A thin plastic spacer behind the magnet can fix a small mismatch.