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Security system using optical sensors

  • US 5,912,619 A
  • Filed: 12/31/1997
  • Issued: 06/15/1999
  • Est. Priority Date: 12/31/1997
  • Status: Expired due to Term
First Claim
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1. A security system monitoring a relative displacement between a first unit and a second unit which are normally in close proximity to each other but which are movable relative to one another, comprising:

  • a first code, generator in the first unit for generating a first coded electrical signal corresponding to a first predetermined coded signal;

    a first transducer in the first unit to which said first coded electrical signal is supplied by said first code generator, said first transducer being responsive to said first coded electrical signal to convert said first coded electrical signal into a signal transmitted toward said second unit;

    a first transducer in the second unit receiving a signal transmitted from said first unit and for converting said received signal back into an electrical signal;

    a second code generator in said second unit to, which said an electrical signal from the first trasducer in the second unit is supplied, said second code generator determining if the electrical signal supplied to it corresponds to said first predetermined coded signal and, if so, said second code generator generating a second coded electrical signal corresponding to a second predetermined coded signal;

    a second transducer in the second unit to which said second coded electrical is supplied, said second transducer being responsive to said second coded electrical signal to convert said second coded electrical signal into a signal transmitted toward said first unit; and

    ,a second transducer in the first unit receiving a signal transmitted from said second unit and converting said received signal back into an electrical signal, said first code generator determining if the electrical signal supplied to it corresponds to said second predetermined coded signal, failure of said first unit to receive said second predetermined coded signal from said second unit indicating either that said first and second units are no longer in close proximity with each other, or that someone is trying to compromise the security system, either condition being an alarm condition for which an appropriate alarm is produced by said security system.

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