<p>Earphone apparatus (10) comprising: a transducer (40)(50)(90)(100) used in processing an audio signal, generating an acoustic output to a user, or tracking movement of a head- mounted part of the earphone apparatus (10); wherein the transducer (40)(50)(90)(100) is further configured to provide to a signal processor (70) an input signal for altering operation of the earphone apparatus (10) or a device connected to the earphone apparatus, the input signal being generated in response to a predetermined user interaction with the earphone apparatus (10) detectable by the transducer (40)(50)(90)(100).</p>
