Make bases to make up with 2-8 inductors, 2 microcomputers, colored liquid crystal display, buzzer, crystal dragon or perfume box. When moving backward, can examine barrier distance recently after going out with the car, show of rejecting in liquid crystal with figure, voice, position 3 function, 3 piece the positions the indicated numbers behind car in the barriers position (Left deviation, in, right) remind driver of according to showing there aren't situation that come out, Guarantee the security.