The invention relates to a method for reduction of the power consumption of a mobile data memory with a non-contact data transmission by means of a read/write device. According to the invention, the mobile data memory, containing at least one energy store and user, is supplied, at least during a cyclic inactive idle mode, with a first clock frequency from a first oscillator and, for data receipt at least during a cyclic request time, with a second higher clock frequency from a second oscillator. The second clock frequency is determined above all for data modulation of a received signal, obtained from the reception antenna or from a combined transmission/reception antenna on the mobile data memory. The invention further relates to a mobile data memory and an identification system with at least one read/write device and one mobile data memory. The advantage of requiring no battery exchange during the life of the mobile data memory is thus conferred.