A control unit, connected to a telephone, sends tone signals to a central dictating/recording unit in response to a user pressing buttons on an auxiliary keypad. The auxiliary keypad, in the form of a thin, membrane-type switch unit, adheres to the back of the telephone handset. A substitute coil cord...http://www.google.es/patents/US5598463?utm_source=gb-gplus-sharePatente US5598463 - Remote terminal for central dictating system
