Monitoring system for remote units

  • US 5,708,417 A
  • Filed: 12/16/1993
  • Issued: 01/13/1998
  • Est. Priority Date: 12/16/1993
  • Status: Expired due to Fees
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First Claim
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1. A monitoring system for monitoring a plurality of mobile units located randomly about a selected security area, and comprising:

  • a set of modules for monitoring the respective said units each including a housing formed with an interior compartment, a signal generator in said compartment programmed to generate a proximity signal, a condition sensor in said compartment operative in response to a selected security condition of said each module to generate a detector flag signal, a battery in said compartment and in circuit with said generator and said sensor, a transmitter and an antenna in said compartment and in circuit with said generator, said sensor and said battery responsive to said proximity signal and said detector flag signal to generate a radio frequency status signal, an encoder in said compartment and in circuit with said transmitter and said antenna responsive to said radio frequency status signal to encode said radio frequency status signal with a code signal unique to the individual modules of said set and with said detector flag signal to produce an encoded radio frequency signal, said transmitter operative in response to said encoded radio frequency signal to cause said antenna to transmit said encoded radio frequency signal at a signal strength equal to but not exceeding a predetermined magnitude for a distance up to but not exceeding a selected distance bounded by said selected security area;

    a local receiver responsive to the respective said encoded radio frequency signal of a signal strength equal to or greater than but not less than said predetermined magnitude to generate a respective receiver signal characteristic of the respective said encoded radio frequency signal; and

    a computer coupled to said receiver and responsive to the respective said receiver signal to generate an alarm signal, said computer including a discriminator responsive to said receiver signal to decode said code signal from said encoded radio frequency status signal, and a monitor responsive to said code signal to identify the module emitting said proximity signal and said detector flag signal.

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