Viper 508D Directed Invisibeam Field Disturbance Sensor Protect your vehicle with the Viper 508D Directed Invisibeam Field Disturbance Sensor which detects moving high-density objects. Viper 508D Directed proximity sensor detects motion events using RF (radio frequency) field disturbance technology. It emits a radio wave and looks for any disturbances in the wave, which if detected can trigger a warn away signal or a full trigger of your car security system. The 508D is one of the most accurate motion sensors in the car security market, and is a great addition to any security system. The Directed 508D proximity sensor is perfect for use in convertibles so you can arm your car with the roof down and rest assured that if someone reaches into the vehicle the security system will trigger. The 508D can also be used for standard roof vehicles, for times you wish to arm the vehicle with the windows down, if someone reaches in your alarm will trigger. This sensor features a dual sensitivity adjustment feature, where you can adjust the inner and outer fields (inner field is full trigger, outer field is warn away).