A signal transferring device adapted to connect to a communication device via a network cable, includes a network port, a third port, a decoder circuit and a signal strength indicator unit. The network port is connected to a communication device via a network cable. The third port is different from the network port and connected to a plurality of signal lines and a ground line of a main board of the communication device via the network port. The decoder circuit is connected to a power line, a ground line and at least one first control line of the main body to receiving a signal in relation to a signal receiving strength state of the communication device for generating a signal strength indicator signal. The signal strength indicator unit is connected to the decoder circuit and configured for displaying the signal receiving strength state of the communication device.