ELEGIANT Parking 4 Sensors Car Reverse Backup Rear Buzzer Radar System Kit Sound Alarm 4 sensor system, double CPU and advanced chipset for enhanced coverage and detection (0-2.5m). High sensitivity, anti-freeze and rain proof. With sound alert when the 4 cameras detect dangers. The closer the obstacles, the louder and faster the sound alert. The buzzer sounds in different frequency according to different distances.