Automobile alarm circuit responsive to multi-frequency phenomena

A sensor for detecting theft or tampering of an automobile comprising a piezo-electric element for producing an output voltage in response to vibrations of said automobile, said piezo-electric element having one side thereof attached to a rigid base member, said base member attached to the automobile body;

• a weight adhered to the opposite side of said piezo-electric element;
• a low-pass filter for receiving the output voltage of said piezo-electric element and for providing an ultra low frequency output signal within the range of 1-5 Hz, said ultra low frequency output signal corresponding to vibrations of said automobile body;
• a band-pass filter for receiving the output voltage of said piezo-electric element and for providing a low frequency bandpass output signal having a center frequency within the range of 30-50 Hz, said bandpass signal corresponding to vibrations of said automobile body;
• comparator means for receiving said ultra low frequency signal and said bandpass signal, comparing each with a predetermined value, respectively, and for providing an illuminating signal to an indicating means as well as an output signal to an output circuit when either of said ultra low frequency signal or said bandpass signal exceeds said predetermined value.