(19)
(11) EP 0 575 753 A3

(12) EUROPEAN PATENT APPLICATION

(88) Date of publication A3:
16.08.1995 Bulletin 1995/33

(43) Date of publication A2:
29.12.1993 Bulletin 1993/52

(21) Application number: 93108236.6

(22) Date of filing: 21.05.1993
(51) International Patent Classification (IPC)5: G07C 9/00, G07C 1/20
(84) Designated Contracting States:
DE ES FR GB IT SE

(30) Priority: 16.06.1992 US 899558

(71) Applicant: MOTOROLA, INC.
Schaumburg, IL 60196 (US)

(72) Inventors:
  • Anderson, Neal R.
    Mesa, Arizona 85202 (US)
  • Malone, Hugh R.
    Phoenix, Arizona 85018 (US)
  • Bjornholt, John E.
    Mesa, Arizona 85203 (US)
  • Boyle, Philip J.
    Tempe, Arizona 85284 (US)

(74) Representative: Hudson, Peter David et al
Motorola European Intellectual Property Midpoint Alencon Link
Basingstoke, Hampshire RG21 7PL
Basingstoke, Hampshire RG21 7PL (GB)


(56) References cited: : 
   
       


    (54) Electronic monitoring system


    (57) An electronic monitoring system (10) for monitoring a large number of inmates confined in an institution is described. Each inmate wears a transmitter (14) which broadcasts an RF signal (18) at random times within a predetermined interval. Reference transmitters (16) positioned at known locations provide calibration so that local transmission anomalies and system variations are accounted for. The transmitted signals (18) contain a common code and also codes unique to each individual transmitter (12). Multiple receivers (22) positioned at known locations receive the transmitted signals (18). The relative times of arrival of the inmate and reference transmitter signals (18) at the multiple receivers (22) are used to determine the location of the inmate transmitters (14). The inmate transmitters (14) may also broadcast an intermittent acoustic signal (15) which is sensed by detectors (17) on the reference transmitters (16), which then transmit a tagged RF signal (18) indicating receipt of the acoustic signal (15). The system (10) provides updated inmate headcount and location about every second.






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