A first communication device 200 comprises a low frequency (LF) transmitter 210 that wirelessly transmits a first authentication signal 513, and a transmitter 220 that wirelessly transmits a second authentication signal 521. A second communication device 300 comprises a LF receiver 310 that receives the first authentication signal 513, and a radio frequency (RF) receiver 320 that receives the second authentication signal 521. A processing unit 240 of the first communication device 200 is linked to a processing unit 340 of the second communication device 300 to perform suitable-time processing when at least one authentication signal received by the receiver of the second communication device is not delayed for a prescribed time with respect to prescribed reference and perform unsuitable-time processing when at least one authentication signal received by the receiver of the second communication device is delayed for the prescribed time with respect to the prescribed reference.
