Reinstall the battery compartment door. Secure with the screw {picture #3). INSTALL THE BATTERY IN THE CONTROLLER A standard 9V Alkaline battery (sold separately} provides power to the controller, Remove the battery door by unscrewing the screw on the back and lifting the door off. {picture #5). install the battery. Be sure on battery is in comet position, Reinstall battery door & rescuer with the SCREW.