This circuit was found in the July 1995 issue of Electronics Now magazine. The integrated circuit is an RCA-era type. The triac must be equipped with a heat sink.
When the sensor is activated the relay turns on powering na external load such as a buzzer siren...
Found in a book on transistors from the 50's. This receiver is very sensitive and features...
Found in 1965s General Electric documentation, this circuit is intended for the control of servos...