This buzzer trigger can be used for small alarms. We find it in an 80’s American documentation. The supply can be done with voltages from 3 to 18 V.
This circuit simulates an inductor. Or operational amplifier of old type, but a configuration is...
This circuit for the logic control of the 555 in a power supply was found in the October 1989...
This traditional configuration from a 1980 publication shows how a reed relay is used to control a 240...