These devices mount in a wall box and turn your lights on and off based on motion detected in the room. (Occupancy sensing.)
Be sure the device you purchase has the mode you want. (For instance: Automatic On, Timed off.) Devices made for California Title 24 do not have an option for "automatic on." That feature is not allowed under Title 24. The motion detector's only function is to turn the light off once the room is vacated.