The Long-Range Door and Window sensor is looking for a ¾ inch or greater separation between the transmitter and magnet for it to trigger an alarm
Be sure to verify when the door is closed that the arrows on the two pieces are perfectly aligned, within a thumb’s width and flush.
Ensure there is no play (movement) in the door or window when it is closed.
Check that both the transmitter and magnet are mounted on the door or window and frame respectively