A signal monitoring circuit includes a plurality of sensors, a meter chip, a micro control unit (MCU), and a multiplexer. The sensors are adapted for collecting electrical signals of an electrical system, and each of the sensors correspondingly generates an output signal. The multiplexer is adapted for receiving the output signal of each of the sensors. The MCU controls the multiplexer to selectively output one of the output signals. The meter chip receives the selected one of output signals from the multiplexer and generates corresponding meter signals to the MCU.