The distance between the vehicle and an obstacle is measured by way of ultrasonic signals and audibly signalled by a warning tone. This tone sequence changes continuously corresponding to the distance between vehicle and obstacle, indicating to the driver the distance to the obstacle. The shorter the distance of the vehicle from the obstacle the faster the tone sequence. A continuous tone sounds at a distance of less than 25 cm. To distinguish the sounds, the pitch is different at the front and rear. In addition to the audible signal, depending on the vehicle and vehicle equipment, the distance.
