An audio system comprises a headset (10) comprising a pair of earpieces (20)(30) positionable with respect to the user's ears so that, in use, the user is inhibited from hearing sounds from the user's environment, at least one of the earpieces having a transducer (50) for reproducing sounds from an input audio signal; a microphone (70) for generating a captured audio signal representing captured sounds from the user's environment; a detector (100) for detecting the presence of any of a set of one or more characteristic sounds in the captured audio signal; and a controller (110) operable to transmit sounds from the user's environment to the user in response to a detection that one or more of the set of characteristic sounds is present in the captured audio signal.