A buzzer is an audio signaling device that generates sound from an incoming electrical signal. Buzzers can be mechanical, electromechanical, or piezoelectric (piezo). They are used in alarm devices, timers, and to confirm user input such as a mouse click or keystroke. 
A big buzzer is a general purpose piezo buzzer that can be used in: 
Alerting and alarming circuits
Rever horns
Kids toys
Big buzzers can operate in a wide range of voltages (9V to 24V). They have the following characteristics: 
Long life
Stable performance
High quality
Small cubage
Low wastage
High voice
Diameter of 38mm
Height of 22mm
2 mounting holes
2 wires
Rate voltage of 12v DC
Operating voltage of 3 - 24v
Sound pressure level of 95