Strong authentication tokens for generating dynamic security values having an acoustical input interface for acoustically receiving input data are disclosed. The tokens may also include an optical interface for receiving input data and may have a selection mechanism to select either the acoustical or the optical input interface to receive data. A communication interface may be provided to communicate with a removable security device such as a smart card and the token may be adapted to generate dynamic security values in cooperation with the removable security device. The acoustic signal received by the token may comprise a plurality of modulated carrier frequencies whereby each carrier frequency has been modulated with a data signal representing the full input data such that the input data are redundantly emitted over more than one modulated carrier frequency.