This is buzzer circuit easy to build with small size,cheaper using normal transistor and small piezo speaker can use for 3V to 12V as use parts resistors[...]
Use low voltage so safe. I am boring old buzzer. When use AC line, danger of leakage power in the heavy rain, 3 circuits can help you!.. .......
For learn about MOSFET. I recommend Time Delay circuit easy to make and long time and a few parts than normal transistor
Often drivers forgot to turn off lights when parking. They cannot start the machine, ran out battery. This Headlight Warning buzzer circuit can help.