Method for ultrasound surveillance of spaces, particularly with regard to motor vehicles

In a method for ultrasonic surveillance of spaces, an ultrasonic transmitter is used which radiates reproducible transmit pulses into the space, and an ultrasonic receiver which receives the reflection signals triggered by these pulses. Both processes occur simultaneously so that an interference field is produced in the surveillance space. With reference to the beginning of the transmitting period, measurement levels are recorded at defined measuring times and compared with one another. An alarm transmitter is activated or kept deactivated in accordance with the result of the comparison. To eliminate false alarms due to thermal effects in the surveillance space, it is proposed to allow the measuring periods for two measurement profiles to begin in each case only after the interference field has settled. During the evaluation, the measurement profiles are first superimposed above one another, with reference to the same measuring time, and then shifted in parallel with respect to one another step by step in the direction of their measurement level, with the aim of achieving the best-possible match between them. The deviations from matched measurement profiles obtained section by section are used as criterion for the case of an alarm.