Remote controlled civil defence warning system - passes alarm signals through public switched telephone network to reach remote terminals

摘要

The remotely-controlled civil defence warning system employs the public switched telephone network to reach remote terminals. The telephone lines connecting the terminals to their nearest switching centre can be changed over from telephone-mode to remote-signalling mode. The switching centres are linked by trunks. The changeover signal is sent from a remote station. Depending on the level of urgency, an engaged line may be interrupted to effect the changeover of the warning may be held over until the line becomes free.