An electronic device includes a backup power supply unit, a first power management unit, a switch, a voltage detection unit, a processor and an electronic module. The first power management unit is coupled to the backup power supply unit and an external power supply unit. The switch is coupled to the first power management unit. The voltage detection unit is coupled to the external power supply unit and the switch. The processor is coupled to the voltage detection unit. The electronic module is coupled to the switch and the processor. When a voltage level of the external power supply unit is lower than a first predetermined level, the voltage detection unit outputs a detection signal. The switch is controlled by the detection signal to open to stop supplying power to the electronic module. The processor is controlled by the detection signal to execute a shutdown process.