Indicated for activation by microcontrollers, this circuit was found in the Radio Electronics magazine of December 1987. The MOSFET can be of any type according to the buzzer.
This basic configuration can be found in a lot of articles on this site. In this case, the relay...
This circuit is from American documentation from the 1980s. The transistors are general purpose...
The circuit is simple, as it uses only one transistor and a relay that can be MC2RC1 or MC2RC2,...