Features: 1.Based on the reflection principle of electromagnetic wave 2.Detect and indicate the distance of obstacles behind cars 3.Detection in all directions without dead angle 4.Easy installation,totally built-in mounting 5.Totally built-in installation with no bad effect to the car appearance 6.The sensor antenna is installed inside the bumper, no need for drill on the bumper 7.During approaching to an obstacle, the electronic unit activates the acoustic signaling with 3 types of signals a.A continuous sound of "beep" approximately between 0-0.3m b.A short interval sound of "beep" approximately between 0.3-0.5m c.A long interval sound of "beep" approximately between 0.5-0.7m