How Do Vehicle Backup Sensors Work?
Most backup sensors transmit ultrasonic signals that reflect off of an object.  The reflected signal is received by the sensor which measures the time between transmission and reception.  Multiplying half the time by the speed of sound yields the distance to the object. For example if the round trip time is measured to be 0.018 seconds, and the speed of sound is 1100 feet/second, the distance is found by multiplying 0.009 (half the time) by 1100 which yields 10 feet.