Buzzer

When powered with DC, a buzzer produces a tone, giving a circuit an audible output in place of, or alongside, a lamp or LED. Buzzer circuits in the community are mostly alarms and indicators: a push-button doorbell, a beep when a relay or transistor switches, a warning in car and security wiring, and a pulsing tone driven by a 555 timer in astable mode. For example, "Beeper with indicators" sounds a buzzer through a relay while LEDs show the state.