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Remotely responsive motion detector

  • US 4,144,529 A
  • Filed: 05/20/1977
  • Issued: 03/13/1979
  • Est. Priority Date: 05/20/1977
  • Status: Expired due to Term
First Claim
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1. A security device adapted to monitor a secured area for the presence of an intruder comprising:

  • an oscillator including a tank circuit coupled to respond to the capacitive and inductive field changes associated with said intruder, said oscillator further including a constant current device tied to said tank circuit for maintaining the frequency thereof substantially constant and for providing amplitude changes in the output signal of said oscillator in response to said capacitive and inductive field changes associated with said intruder;

    bandpass filter means connected to receive said output signal from said oscillator means said bandpass filter means being conformed to produce a filtered signal corresponding to the frequency components of said output signal which are in the frequency domain of the field changes of said intruder;

    differentiating means connected to receive said filtered signal for producing a switching signal when the rate of change of said filtered signal exceeds a predetermined level;

    transmitting means connected to be rendered operative by said switching signal for producing a radio signal upon the receipt of said switching signal; and

    receiving means conformed to respond to said radio signal for producing an audio signal indicative thereof.

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