Abstract: A gas sensing device has a sampling chamber for containing a gas to be sensed, with a gas sensing element with the chamber for providing an output signal which varies in response to the presence of the gas in the chamber. An orifice, or other restriction, permits gas flow between the interior and the exterior of the chamber and a pump, e.g. in the form of a heater, displaces a sample of the gas through the restriction into the interior of the chamber for sensing by the sensing element and subsequently displaces gas from the interior to the exterior of the chamber.