Features: 1) With waterproof designing, control box can be installed outside the compartment. RF data transmission between display and control box eliminates tough wiring work especially for long vehicles. Equipped with S-11 sensors, which can be installed underneath at the back, the system is an ideal anti-collision solution for buses, trucks and recreational vehicles. 2) Available sensors quantity: 4 rear sensors 3) Audible distance indication 4) Distance and sound a) 1.50 - 0.80m: Bi, Bi, Bi b) 0.80 - 0.40m: Bi Bi BiBi (the closer, the faster) c) 0.40 - 0m: Bi... (solid beeping)