A signal input apparatus includes a hand-held device and a receiving device. The hand-held device includes a sensor for outputting a signal, a first data port coupled to the sensor, and a wireless signal transmitter coupled to the sensor. The receiving device includes a second data port and a wireless signal receiver. When the receiving device and the hand-held device are separated, the hand-held device outputs the signal through the wireless signal transmitter, and the receiving device receives the signal through the wireless signal receiver. When the receiving device and the hand-held device are integrated, the first data port and the second data port are electrically connected, the hand-held device outputs the signal through the first data port and the receiving device receives the signal through the second data port.