Easy to install on windshield or number plate , no need detach bumper. it just takes around 30 minutes to finish the installation,save time and money Through installing 1pcs of 77GHz millimeter wave sensors on the car rear windshield , when the car is moving, if any moving object closer to blind area( 3 meter from right and left side ,30 meters from behind）,the object will be detected by system sensor , the LED indicator will turn on and keep shining for reminding driver, in this condition, if the driver wants to change the lane, the buzzer will beep sounds for reminder. .