A radio frequency identification (RFID) system has a reader, a first antenna, a second antenna and a transponder. The first antenna is electrically connected to the reader, and the reader is used to generate a control signal and transmit the control signal through the first antenna. The second antenna is used to receive the control signal. The transponder is integrated into an electronic element of a portable electronic device and is electrically connected to the second antenna. The transponder is arranged to select a data signal according to the control signal and transmit the data signal to the reader through the second and first antennas.