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Passive type crime-preventing infrared sensor provided with a mechanism of monitoring an obstruction for the visual field

  • US 4,982,094 A
  • Filed: 06/23/1988
  • Issued: 01/01/1991
  • Est. Priority Date: 10/31/1986
  • Status: Expired due to Term
First Claim
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1. A passive-type, crime-preventing infrared sensor, comprising:

  • first detecting means for detecting infrared radiation from an object in a visual field to be monitored;

    a first electrical alarm circuit means for providing an alarm in response to detection of a signal output from said first detecting means;

    second detecting means for detecting infrared radiation from an object approaching said first detecting means independently of said first detecting means, thereby detecting an obstruction of said first detecting means; and

    a second alarm circuit means for providing an alarm response to detection of a signal from said second detecting means, said second alarm circuit being electrically isolated from said first alarm circuit.

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