The OSW-U-0721 is a self contained, energy saving, motion-sensing lighting control which replaces a conventional wall switch and utilizes ultrasonic technology to detect room motion. The sensor produces a low-intensity, inaudible sound to detect occupancy in a room. Changes in the sensor’s acoustic wave caused by motion, such as walking into a room, reaching for a telephone or swiveling in a chair, will cause the lights to turn ON. The sensor does not respond to audible sound. Wall switches are ideal for smaller spaces where you will not have obstructions of line-of-sight due to switch location, room orientation or furniture placement.