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
This is IC 4060 Timer circuit. When rises time that is set, Suppose set 5 minutes time. after all time to 5 minutes. the circuit will emit a sound of buzzer once. [...]
Often drivers forgot to turn off lights when parking. They cannot start the machine, ran out battery. This Headlight Warning buzzer circuit can help.
The simple low voltage tester circuit using LM339,can use Battery voltage monitor for voltage sources that problems, by LED display and alarm sound.
The 2 tone doorbell circuit, which is an electronic buzzer types,but them has melodic sound than general electric bell. People have seen two tone bell sound