Power device

A power device comprises a buzzer, a control unit, and a driving circuit. The control unit records a plurality of PWM frequencies corresponding to various pitches, and is configured to generate a PWM signal according to an alert sound corresponding to a determination result, and to change the frequency of the PWM signal according to at least two pitches of the alert sound. As to the driving circuit, it is configured to drive the buzzer to emit the alert sound according to the PWM signal.