These systems advise you via audible and/or visual indicators as to how close you are to objects behind or in front of you. The goal is to prevent damaging your bumper in tight situations or where the sight-lines are poor. Most systems use ultrasonic sensors to detect the distance to close objects.
Systems are available for just the front, back, or both areas. A typical 8 sensor system gives total front and back coverage, but if you don’t need full coverage, you can save money by using a system with fewer sensors. Systems also come with wired and wireless models, where the wireless models are easier to install. All require significant work to install, such as drilling bumpers to fit the sensors, wire routing through the car, and multiple electrical connections.
Some systems also offer the option of two sensors instead of four, which reduces the drilling and wiring work. For the front, this means two can be mounted in the front black nose-cone area, avoiding the need for painting the sensors (if already black).
Our own step-by-step installation guide: