An audio headset comprising: a microphone; one or more speakers, each configured for use with a human ear; an audio connector comprising: a microphone output pin and one or more speaker input pins respectively connected to the one or more speakers; a microphone line between the microphone output pin and the microphone; a ground line; a plurality of input devices (114, 115, 116) in communication with the microphone line; and a plurality of respective depletion mode devices (F1, F2, F3) corresponding to the input devices (114, 115, 116); a first circuit configured for active signalling on the microphone line; a second circuit comprising one or more devices having a predetermined impedance, the second circuit being configured for passive signalling on the microphone line, wherein the plurality of depletion mode devices (F1, F2, F3) is connected between the ground line and the second circuit; and a processor configured to control the plurality of depletion mode devices (F1, F2, F3), the processor being in communication with the plurality of input devices (114, 115, 116), the processor being further configured to: determine a present signalling mode; when the present signalling mode comprises an active signalling mode, generate active signals on the microphone line using the first circuit when one or more of the plurality of input devices (114, 115, 116) are actuated; and, when the present signalling mode comprises a passive signalling mode, change an impedance on the microphone line by changing connections in the second circuit when one or more of the plurality of input devices (114, 115, 116) are actuated; the processor being further configured to: activate the second circuit by controlling the depletion mode devices (F1, F2, F3) to a conducting state; and deactivate the second circuit by controlling the depletion mode devices (F1, F2, F3) to a non-conducting state. a microphone; one or more speakers, each configured for use with a human ear; an audio connector comprising: a microphone output pin and one or more speaker input pins respectively connected to the one or more speakers; a microphone line between the microphone output pin and the microphone; a ground line; a plurality of input devices (114, 115, 116) in communication with the microphone line; and a plurality of respective depletion mode devices (F1, F2, F3) corresponding to the input devices (114, 115, 116); a first circuit configured for active signalling on the microphone line; a second circuit comprising one or more devices having a predetermined impedance, the second circuit being configured for passive signalling on the microphone line, wherein the plurality of depletion mode devices (F1, F2, F3) is connected between the ground line and the second circuit; and a processor configured to control the plurality of depletion mode devices (F1, F2, F3), the processor being in communication with the plurality of input devices (114, 115, 116), the processor being further configured to: determine a present signalling mode; when the present signalling mode comprises an active signalling mode, generate active signals on the microphone line using the first circuit when one or more of the plurality of input devices (114, 115, 116) are actuated; and, when the present signalling mode comprises a passive signalling mode, change an impedance on the microphone line by changing connections in the second circuit when one or more of the plurality of input devices (114, 115, 116) are actuated; determine a present signalling mode; when the present signalling mode comprises an active signalling mode, generate active signals on the microphone line using the first circuit when one or more of the plurality of input devices (114, 115, 116) are actuated; and, when the present signalling mode comprises a passive signalling mode, change an impedance on the microphone line by changing connections in the second circuit when one or more of the plurality of input devices (114, 115, 116) are actuated; the processor being further configured to: activate the second circuit by controlling the depletion mode devices (F1, F2, F3) to a conducting state; and deactivate the second circuit by controlling the depletion mode devices (F1, F2, F3) to a non-conducting state. activate the second circuit by controlling the depletion mode devices (F1, F2, F3) to a conducting state; and deactivate the second circuit by controlling the depletion mode devices (F1, F2, F3) to a non-conducting state.