Battery in motion sensor for ADT system?

When I open the sliding glass door, there is a rapid beeping only stops when I hit the buttons on the keypad .I have turned the chime off and when the door is opened , it still beeps. SOmetimes I can get it stopped and then it starts up again...like there is a short...only with that one door.
I couldn't see a battery in the motion sensor...or is that even related to the problem?

need help in Missouri,