An exemplary power-saving system for a computer includes a sensor connected between a standby power pin and ground, an amplifier, two resistors connected in series between the standby power pin and ground, a comparator, an electronic switch, and an MPU. The amplifier has two amplifier input terminals respectively connected to an output of the sensor and ground, and an amplifier output terminal grounded via an integrator. The comparator has two comparator input terminals respectively connected to the integrator and a node between the two resistors, and a comparator output terminal connected to a first terminal of the electronic switch. A first pin of the MPU is connected to a second terminal of the electronic switch, and connected to the standby power pin via a third resistor. The MPU has second and third pins connected to a system power pin and the BIOS of the computer respectively.