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Alarm system

  • US 4,162,488 A
  • Filed: 03/11/1977
  • Issued: 07/24/1979
  • Est. Priority Date: 03/11/1977
  • Status: Expired due to Term
First Claim
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1. An alarm system for monitoring conditions at a plurality of protected premises comprising:

  • switching means having a primary port and a plurality of secondary ports and responsive to successive appearances of a predetermined signal at its primary port for sequentially establishing connections between said primary port and each of said plurality of secondary ports;

    central monitoring station apparatus connected to said switching means primary port, said central monitoring station apparatus including;

    means for successively generating said predetermined signal at equally spaced predetermined intervals;

    means operative at the termination of each occurrence of said predetermined signal for transmitting a START signal over the connection established by said switching means;

    means for detecting predetermined tones received over said connection after the termination of said START signal; and

    means responsive to a tone absence for recognizing an alarm condition; and

    a plurality of transponder units each located at a respective protected premises and each connected to a respective one of said switching means secondary ports, said respective protected premises including a plurality of protected zones, with one or more sensor elements disposed at each of said protected zones for providing status indications of each of said protected zones, each of said transponder units including;

    clock means responsive to receipt of said START signal over said switching means connection for defining a plurality of time slots each corresponding to one of said protected zones;

    means for transmitting selected ones of said predetermined tones during corresponding ones of said plurality of time slots over said connection; and

    means responsive to an indication from a sensor element of said alarm condition in one of said protected zones for inhibiting the transmission of tons in the time slot corresponding to said one protected zone, so as to produce said tone absence for recognition by said recognizing means in said central monitoring station apparatus.

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