Pass & Seymour Dual technology wall switch sensors offer a powerful "one-two" combination for optimum energy management. These switches give you the most sensitive and consistent way to manage lighting energy consumption in a wide variety of commercial applications from small offices and executive suites to conference rooms and break rooms. They do it through dual technology design that combines both passive infrared (PIR) and ultrasonic technologies to give high sensitivity to small and large movements and wide dense detection, tiring lights On and OFF based on a more accurate, dependable sensing of room occupancy. And installation/switchout is fast and easy with compact product design that fits into existing boxes. Most importantly, the combination of PIR and ultrasonic technologies in both the WDT100 and WDT200 gives you two ways to detect occupancy and turn lights on automatically, then turn them off when no occupancy is detected. PIR technology detects the infrared energy from a human body in motion and the ultrasonic technology spreads coverage over a wider area and detects smaller movements to time the ON/OFF function more efficiently.