A switch circuit comprising a mechanical switch having two contact elements, the switch being operable to bring the two contact elements into physical contact and thereby output an analogue switch signal representative of operation of the switch and a sigma-delta modulator arranged to receive the analogue switch signal and to output a digital switch signal in dependence thereon, the sigma-delta modulator having a frequency response such that it can suppress a relatively high frequency component of the analogue input signal and thereby effectively debounce the output of the switch.