A medical device (20) includes a case (32), having a front surface that is configured to be brought into contact with a body of the living subject (24). A microphone (34) is contained in the case and configured to sense acoustic waves emitted from the body and to output an acoustic signal in response thereto. A proximity sensor (56) is configured to output a proximity signal indicative of contact between the front surface and the body. At least one speaker (49) is configured to output audible sounds. Processing circuitry (50) is coupled to detect, in response to the proximity signal, that the front surface is in contact with the body, and in response to the detected contact, to process the acoustic signal so as to generate an audio output and to convey the audio output to the at least one speaker.