We found this circuit in the September 1971 Radio Electronics magazine. The SCR can be any of the 106 series and the buzzer can be replaced by a relay according to the supply voltage.
This transmitter, indicated for espionage applications, is permanently powered by the power grid....
This signal follower or signal tracer was found in an English publication from 1989. The...
This circuit appeared in a Radio Electronics magazine in March 1962. The circuit uses two...