The invention discloses a device for communicating with a portable data medium using at least a power signal (AL) supplied by an electric energy source (4), a control signal (SC1), and a data transmission signal (I/O), characterised in that it comprises: means (5) for interrupting the power signal (AL) to the medium from the source if the latter does not co-operate with the device (1); means (8) for storing electric energy received from the source and for supplying the said power signal to the medium when the source does not supply same; means for data processing (3) arranged to ensure transmission of the said signals (AL, SC1, I/O) to the medium according to a predetermined sequencing, as well as for detecting the interruption of the power signal (AL) from the source, then for triggering the interruption of the other signals (SC1, I/O) according to the said predetermined sequencing during the supply of the power signal from the energy storage means.