Abstract: A gas detection apparatus having a microprocessor control circuit mounted within a housing chamber which is operable for processing input signals associated with measured gas levels and generating output signals corresponding to same to the output port. An interchangeable electrochemical sensor device is removably disposed within the chamber via an access opening of the housing, the sensor being operable for sensing and measuring gas levels and generating the input signals to the microprocessor circuit. An elastomeric connector unit is removably and sealingly disposed between interfacing contact surfaces of the sensor and control circuit via the access opening. The connector unit provides a conductive path between the microprocessor circuit and the sensor device and electromagnetic shielding therebetween.