Here is the simple circuit that starts blowing the car horn whenever your car is in reverse gear. This circuit will produce a musical sound when ever your car is in reverse direction to alert the other vehicles. As most of the people have their own vehicle so I suppose this circuit is very useful for them.  This circuit will also avoid the chances of accident  at blind turn, as speeding vehicle get a alert by hearing the musical sound that a car is taking reverse and he will slow its speed.This simple circuit is based on melody generator IC UM66, transistor and few more components. This car reverse horn circuit can be used with any vehicle having 12V battery. Whenever user reverses its car, brake switch gets connected to power supply and circuit will get power supply for its working.  And the transistor T4 connected through a diode gets power supply and start conducting.