Geartist (TM) GTS8500B Car Parking Sensor Kit Reverse Backup Radar Sound Alert + 4pcs Waterproof Rear Sensors (GTS8500B) 4 sensor (22mm, 2.3m cable) system, double CPU and advanced chipset for enhanced coverage and detection. With sound alert when the 4 cameras detect dangers. The closer the obstacles, the louder and faster the sound alert. Step-up Buzzer alarm, detective distance from 1.8m to 0.3m. Anti-freeze and waterproof function, easy installation, there are only a few steps to install it.