Power device

A power device comprises a speaker, an audio circuit and a control unit. The speaker comprises a first input terminal, and is configured to emit sound according to the signal received by the first input terminal. The audio circuit comprises a first output terminal, and the first output terminal is electrically coupled to the first input terminal. The audio circuit stores a plurality of audio files, and each audio file corresponds to an alert sound. Each alert sound comprises at least two pitches, and each pitch corresponds to a PWM frequency. The audio circuit is also configured to select one of the audio files according to a control command, generate a first PWM signal according to the selected audio file, and output the first PWM signal from the first output terminal. The control unit is configured to generate a corresponding control command according to a determination result.