Buzzer
Videos
A buzzer or beeper is an audio signaling device, which may be mechanical, electromechanical, or piezoelectric. Typical uses of buzzers and beepers include alarm devices, timers, train and confirmation
Piezoelectric disk beeper
Interior of a readymade loudspeaker, showing a piezoelectric-disk-beeper (With 3 electrodes ... including 1 feedback-electrode ( the central, small electrode joined with red wire in this photo), and an oscillator to self-drive the buzzer.
Timer
Videos
A timer or countdown timer is a type of clock that starts from a specified time duration and stops upon reaching 00:00. It can also usually be stopped manually before the whole duration has elapsed. A
A typical kitchen timer
An electromechanical timer