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Antitheft system with digitally coded signal

  • US 4,559,529 A
  • Filed: 04/15/1985
  • Issued: 12/17/1985
  • Est. Priority Date: 06/29/1983
  • Status: Expired due to Term
First Claim
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1. A security system for detecting the removal of an article from a premises to be protected, the protected premises including at least one exit through which the article may be removed from the protected premises, said security system comprising in combination:

  • (A) a transmitter for transmitting at least one signal in the vicinity of said exit, said signal being transmitted as an electromagnetic radio wave of a predetermined frequency and being transmitted as a plurality of serially coded bits, said serially coded bits being transmitted by said transmitter during a corresponding plurality of successive code bit intervals;

    (B) receiver means carried by said article, said receiver means including;

    i. a receiver for detecting the presence of said signal, said receiver including a filter for passing signals of said predetermined frequency, said receiver being adapted to receive said serially coded bits when said article is brought into the vicinity of said exit;

    ii. processing means for storing a pattern of code bits and being coupled to said receiver for comparing the serially coded bits received by said receiver with the stored code bits to determine whether they match one another, said processing means providing an output signal when said serially coded bits match the stored code bits;

    iii. clocking means for providing clock signals to said processing means to distinguish the plurality of successive code bit intervals; and

    iv. alarm means electrically coupled to said processing means and responsive to said output signal for creating an alarm to assist in the recovery of the removed article; and

    (C) a power supply carried by said article and electrically coupled to said receiver means for supplying electrical power thereto.

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