Abstract: The invention relates to a transmission-reception system, particularly a transmitter-receiver device contained in the bow of an ignition key. When a resonance circuit receives a carrier wave signal from a transmission-reception ECU of a motor vehicle, a microcomputer is switched to an active state by the output of a power circuit that smoothes and rectifies the carrier wave signal. A detector circuit discriminates an enquiry signal supplied together with the carrier wave signal through the resonance circuit portion, and outputs the signal to the microcomputer. In response to the enquiry signal together with random number data, the activated microcomputer changes the bit length of an identification code stored in an EEPROM, on the basis of the received random number data and a predetermined function, and performs the on-off control of an FET of a modulating circuit in a mode corresponding to the bit length-changed identification code.

Abstract: A card body of an IC card is composed of first and second halves connected by a self hinge portion so as to be foldable into halves in such a manner that the surface where a contact is provided comes inside. The first and second halves are provided with a magnet and a magnetic body to hold the IC card folded by magnetic attractive force. When folded, a control section provided in the first half 1a is connected to transmitting-receiving means and a communication control section that are provided in the second half, by the contact and the transmission-reception contact, so that the IC card can function as a non-contact type IC card.