Honeywell Home 997 Ceiling Mount PIR (passive infrared) Motion Sensor is designed to be mounted in small to medium sized rooms between 8' and 12' high. Optimal performance is achieved when the detector is mounted on the ceiling in the center of the protected area. While a single 997 is ideal for sensing motion in rooms up to 30' x 30', multiple detectors are recommended when protecting larger areas like classrooms, meeting rooms, public lobbies and storage areas.