3864674 is referenced by 24 patents and cites 6 patents.

A radio warning system includes emergency condition sensors for actuating respective radio transmitters which are modulated by identification generators to produce identification signals which contain one or more frequencies selected from groups of four frequencies in accordance with selected identifying binary coded decimal digits. A transmitted identification signal is detected by a radio receiver in a mobile unit or central dispatch location to operate a memory and a decimal display unit to indicate the existence and location of the emergency condition until reset by an operator. The transmitters are deactuated by a timing circuit after a predetermined period. Delay circuitry prevents operation of the memory and decimal display unit until the identification signal has been received for a predetermined continuous duration.

Emergency Radio Warning System
Application Number
Publication Number
Application Date
December 18, 1972
Publication Date
February 4, 1975
Martin Stephen J
Worsham Robert
O Brien Anthony A
H04q 11/02
H04b 07/00
G08B 25/01
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