An audio subsystem for a mobile device comprising at least one speaker, the audio subsystem comprising: an audio source (295 1, 295 2) for generating an audio signal (293, 297); a capacitive proximity sensor comprising a detection circuit configured to generate a sensor output signal representing a distance to a user of the mobile device and a failsafe generator coupled to the detection circuit and configured to generate a sensor status signal indicating an operational status of the capacitive proximity sensor; and a power amplification module (290 1, 290 2) configured to process the audio signal (293, 297) received from the audio source into an amplified audio signal (270, 280) for output by the at least one speaker, the power amplification module (290 1, 290 2) comprising a gain controller responsive to the sensor output signal and the sensor status signal to determine and apply a gain factor to the audio signal (293, 297) based on the distance to the user of the mobile device and the operational status of the capacitive proximity sensor; wherein the failsafe generator is configured to: monitor an operating parameter of at least one internal signal of the capacitive proximity sensor, the operating parameter of the at least one internal signal indicative of the operational status of the capacitive proximity sensor; and generate the sensor status signal based on the operating parameter of the at least one internal signal; monitor the operating parameter of the at least one internal signal over a time interval; if over the time interval the operating parameter of the at least one internal signal is within an expected range, set the sensor status signal to a default control value for the gain controller to apply variable gain to the audio signal (293, 297) based on the distance to the user; and if over the time interval the operating parameter of the at least one internal signal is outside the expected range, set the sensor status signal to an override control value for the gain controller to apply fixed gain to the audio signal (293, 297) independently of the distance to the user. an audio source (295 1, 295 2) for generating an audio signal (293, 297); a capacitive proximity sensor comprising a detection circuit configured to generate a sensor output signal representing a distance to a user of the mobile device and a failsafe generator coupled to the detection circuit and configured to generate a sensor status signal indicating an operational status of the capacitive proximity sensor; and a power amplification module (290 1, 290 2) configured to process the audio signal (293, 297) received from the audio source into an amplified audio signal (270, 280) for output by the at least one speaker, the power amplification module (290 1, 290 2) comprising a gain controller responsive to the sensor output signal and the sensor status signal to determine and apply a gain factor to the audio signal (293, 297) based on the distance to the user of the mobile device and the operational status of the capacitive proximity sensor; wherein the failsafe generator is configured to: monitor an operating parameter of at least one internal signal of the capacitive proximity sensor, the operating parameter of the at least one internal signal indicative of the operational status of the capacitive proximity sensor; and generate the sensor status signal based on the operating parameter of the at least one internal signal; monitor an operating parameter of at least one internal signal of the capacitive proximity sensor, the operating parameter of the at least one internal signal indicative of the operational status of the capacitive proximity sensor; and generate the sensor status signal based on the operating parameter of the at least one internal signal; monitor the operating parameter of the at least one internal signal over a time interval; if over the time interval the operating parameter of the at least one internal signal is within an expected range, set the sensor status signal to a default control value for the gain controller to apply variable gain to the audio signal (293, 297) based on the distance to the user; and if over the time interval the operating parameter of the at least one internal signal is outside the expected range, set the sensor status signal to an override control value for the gain controller to apply fixed gain to the audio signal (293, 297) independently of the distance to the user.