This is typically caused by a mounting issue. Please check the following:
Ensure one piece is mounted on the door or window and the other piece is mounted on the frame
Ensure the arrows (or notches) on the transmitter and magnet are facing each other
The space between both the transmitter (larger piece) and magnet (smaller piece) should not exceed 3/4", or a thumbs width.
Check for any recess in the door/frame. Ensure both pieces are on the same plane