Abstract: A data carrier system allows data to be transmitted and received. The data is transmitted using weak radio waves of suitable frequencies, such as frequencies in a high frequency band (HF) or a very high frequency band (VHF). The transmitters and receivers need not physically contact each other, be located in any particular position, or be oriented in any particular direction. The data carrier system does not suffer deficiencies in electric power supply, and therefore there exists no need to exchange batteries. Individual transmitters and receivers are positively discriminated one from another. The receivers are in the form of a plurality of tags. The transmitters are in the form of a plurality of reader-writers. Both are controlled by microcomputers, and each tag is equipped with a secondary battery as the power source.