05552772 is referenced by 343 patents and cites 9 patents.

Method and apparatus for monitoring the present location of an emergency or general serviceperson, such as a firefighter or a hazardous materials spill clean-up specialist, assigned to perform emergency services at a designated site. The site diameter can be as small as a few meters or as large as several kilometers. The serviceperson's present location can be checked at selected time intervals with time periods ranging from a few hundred milliseconds to thousands of seconds, as desired. The serviceperson wears or carries a location-determining ("LD") unit that receives electromagnetic signals that contain information allowing determination of the present location of the LD unit, and thus of the serviceperson, from three or more signal sources. These signal sources may be FM subcarrier signal transmitters, or may be an integrated combination of FM subcarrier signal transmitters and (1) transmitters for a Loran, Omega, Decca, Tacan, JTIDS Relnav or PLRS or other ground-based system, or (2) transmitters for a satellite-based positioning system, such as GPS or GLONASS, or other broadcast sources. The relative phases or transmission times for the signals from each source are determined and provided for the LD unit. The present location of the serviceperson, or change thereof, is determined and transmitted to a central station at selected interrogation times, or upon occurrence of any of a specified group of other conditions. The central station transmits an alarm signal if one or more of the following conditions is present: (1) the worker's LD is not within the designated site; (2) the central station does not receive transmitted present location information from the LD unit for at least K consecutive interrogation times; or (3) the location of the LD unit changes by less than a selected threshold amount in a time interval of selected length .DELTA.t.sub.change ; or (4) a physiological indicium of the serviceperson is in a danger zone.

Location of emergency service workers
Application Number
Publication Number
Application Date
December 20, 1993
Publication Date
September 3, 1996
John F Schipper
Palo Alto
James M Janky
Los Altos
John Schipper
Trimble Navigation
G08B 23/00
View Original Source