These sensors are rubber housed for durability and can be mounted in painted metal bumpers*. Audible Warnings At approx' 2.0~1.8 metre the buzzer starts to sound slowly As you get closer the buzzer sounds faster At approx' 0.50 metre the buzzer sounds constantly........stop ! *Detection distances vary according to fitted height and obstacles being detected. Note: Reversing sensors are a driving aid and the usual driving precautions should be taken whilst reversing. Sensors may not detect all possible objects/obstructions. Detection distances are approximate. * The cut edge of metal bumpers must be painted to prevent rust. Features:- Rubber outer sensor head shells Bevelled sensor lip to enable correct installation angle Automatically switch on when reverse gear selected 4 bumper mounted sensors Detachable heads for easy service or vehicle repair Control module - 2 wire installation Super loud buzzer 21mm plastic bumper hole cutting tool NB - Additional hole saw is needed for chrome / thick metal bumpers. Finished in matt black - painting not recommended