3760349 is referenced by 20 patents and cites 4 patents.

An emergency warning system is disclosed which includes a transmitter adapted to be mounted in an emergency vehicle, such as an ambulance or police car, and a receiver adapted to be mounted in another vehicle such as a private automobile. The transmitter emits coded signals in response to actuation of the vehicle's siren or other emergency device, and the receiver responds to receipt of only the coded transmitted signals when the emergency vehicle and another vehicle are in close proximity to provide visual or audio signals to the driver of another vehicle to warn him of the proximity of the emergency vehicle. A switch is provided in the receiver to override the audio warning signal received by the driver of another vehicle, and the switch is automatically reset by loss or reduction of signal from the transmitter of the emergency vehicle.

Title
Emergency warning system
Application Number
05/155,117
Publication Number
3760349
Application Date
June 21, 1971
Publication Date
September 18, 1973
Inventor
Leibfreid Russel B
Keister Douglas W
IPC
G08g 01/00
G08G 01/962
G08G 01/965
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