03986119 is referenced by 56 patents and cites 11 patents.

An emergency communication system used by stranded motorists to summon help when travelling on toll roads or other limited access highways. The emergency communication system comprises a portable, self-powered, hand-held transceiver set which transmits coded distress signals and directional signals, when activated, and cycles until reception of an answer back signal. The signals or messages from the portable transceiver are transmitted at incrementally increasing power levels to a single or a plurality of roadside relay stations spaced strategically along a limited access highway or toll road. The relay stations retransmit the signals to a terminal station which has means to decode the signals and determine the location of the repeater station nearest to the stranded motorist. The terminal station also has means for displaying the location of the relay station with the information derived from the decoded signal, and means for generating an answer back signal which is transmitted via the roadside relay station to the portable handset.

Title
Emergency communication system
Application Number
5/429241
Publication Number
3986119
Application Date
December 28, 1973
Publication Date
October 12, 1976
Inventor
Agis Demetrius Valakos
Bethesda
MD, US
Nicholas Howard Hemmer Jr
Poughkeepsie
NY, US
Agent
John G Wynn
J G Cockburn
Assignee
International Business Machines Corporation
NY, US
IPC
H04B 7/00
View Original Source