This is the electronic pet door that automatically opens when a pet approaches. The unit installs in a sliding patio door frame and when a pet wearing the included ultrasonic collar comes within 1' to 10' (the distance is selected by owner) the pet door automatically opens to let the pet in or out. When the pet passes through the door it closes automatically; the door can be set to restrict a pet to only being able to enter or leave the house or to prevent the door from opening. Its rigid aluminum frame, dual pane window made of hermetically sealed, tempered glass, and air-tight pet door that locks with a dead bolt ensure a secure, weathertight barrier. The included lock installs at the base of a sliding door to provide security and allow owners to enter or exit. Fits 77 1/4"-80 1/4" high sliding patio door frames. Plugs into AC.