The parking sensor uses Ultrasonic Sonar to detect objects behind your vehicle. Warning beeps let you know that there is an obstacle behind you. The beeps speed up as you get closer, allowing you to judge distances and avoid accidents. Reversing accidents range from the annoying, to the costly, to the unthinkable. But when you have a Parking Sensor PS-04 you backup with confidence. Parallel parking becomes a breeze, and paint scratches from backing into parking barriers becomes a thing of the past. Most importantly, backing up becomes a whole lot safer.