Civil defence warning system - uses telephone system to transmit signals triggering alarm stations

摘要

A nationwide warning system for alerting the civilian population uses the public telephone system to provide connection and activation of sirens. The system is based upon a centralised control point connecting through sub-stations and branch points. The alarm units that tare distributed nationally are activated when a coded signal is generated. The coded signal consists of frequency samples in the range 1700 to 2040 Hz.