Abstract: An automobile theft sensor has a piezo-electric element adhered at one side to a base member and which generates a voltage in response to vibration of the automobile body, a weight adhered to the opposite side of the piezo-electric element, a silicon rubber coating covering at least a portion of the surface of the piezo-electric element and weight, a low pass filter for receiving the output voltage of the piezo-electric element and for providing an ultra low frequency signal within the range of 1-5 Hz produced by the above mentioned piezo-electric element; and a band pass filter for receiving the output voltage of the piezo-electric element and for providing a low frequency bandpass signal centered on the 30-50 Hz produced by the above mentioned piezo-electric element in response to vibration of the above mentioned automobile body. When either of the filter outputs exceeds a predetermined level it is judged that theft or tampering is occurring.

Abstract: A piezo-electric film is pasted to one surface of an elastic film fixed at the ends and a weight is attached substantially to the middle of the other surface of this elastic film.

Abstract: In this sensor, a weight having a permanent magnet is fitted substantially in the middle of an elastic film fixed at the ends and a hall element or magnetic resistance element is arranged so as to be opposed at a proper spacing to the permanent magnet of the weight.

Abstract: A sensor of the theft and the like of an automobile wherein a thin plate is fixed at one end to a base, an elastic string is stretched between the other end of the thin plate and a supporting plate provided from the above mentioned base, a weight is provided in the middle of the string and a sheet-shaped buffer material, conductive thin plate and piezoelectric element are successively pasted to the above mentioned thin plate.