PURPOSE: To reliably detect intrusion into a vehicle using simple and low-cost parts by providing a processing means which transmits a signal of specified frequency to a reception means inside a vehicle, compares the change in phase in the signal with a predetermined threshold value of change in phase and determines that intrusion into the vehicle interior occurs.
CONSTITUTION: A signal is transmitted from a microphone 16 in the front part of a vehicle to a signal processing circuit including a preamplifier 40, a band- pass filter 42, a low-pass filter 52, zero crossing detectors 44 and 54, exclusive OR gates 46 and 56, D-type flip-flops 48 and 58 and AND gates 50 and 60. In this case, the zero crossing detector 44 generates a high signal when the output signal from the band-pass filter 42 is higher than a reference value and a low signal when it is lower. Then the signal is transmitted to a controller 12, filters 30 and 32, a summing amplifier 34 and to a power amplifier 38 and drives a speaker 18.
RICHIYAADO DEERU IITON
FURANKU BURUUSU UIROTSUKU
JIYON RICHIYAADO BORUFUISU
