Circuits and methods to achieve a switch interface circuit for a single pole, single throw (SPST) momentary push-button switch consuming a few tens of nanoamps whilst the push-button switch is closed, having low impedance input path when the switch is open in order to eliminate RFI interference have been achieved. The two states of the push-button switch, open and closed, maintain a low impedance path to one of the power supplies. The supply current is zero when the switch is open and is minimized whilst the switch is closed. The asynchronous edge triggered detection of the switch event allows an extended switch open to closed transition operation.