Abstract: The invention relates to a method for operating a contactless and batteryless chip card. The chip card is supplied with energy via an alternating field by a write/read unit. The bidirectional data transfer is achieved by modulation of the energy-transmitting alternating field. The chip card includes, inter alia, an antenna coil for receiving the alternating field, an input circuit generating the supply voltage from the coil current, and a voltage detector for detecting blanking gaps in the alternating field. By the method in accordance with the invention the voltage detector compares the two voltages at the coil ends with one another and then supplies an output signal, provided both the voltages are substantially equal in size for longer than a predetermined period. Furthermore, a chip card is described that contains a voltage detector permitting operation according to the method described.