A secure memory device for a smart card with a modem interface comprising a rewritable memory such as an EEPROM, a processing unit or a microprocessor, an on-chip oscillator, an ISO 7816 interface, a one-wire modem interface, and characterized in that both communication interfaces are bidirectional and share the same I/O terminal. The modem interface is exchanging data with the host in the form of a modulated signal by means of a card reader characterized by the absence of processing means.