A gas detector with a selectively adsorbing surface (3) and an acoustic measuring cell (5) is presented. The detector is characterized in that the selectively adsorbing surface (3) and the acoustic measuring cell (5) can be arranged with respect to one another such that gases desorbed by means of thermal desorption from the adsorbing surface (3) reach the acoustic measuring cell (5) and there trigger a pressure wave that can be measured by one or more acoustic pick-ups (13, 14), in particular microphones, which are arranged in the acoustic measuring cell (5). Furthermore, a corresponding method is provided. The detector is particularly suitable for measuring contaminants in interior spaces and ventilation systems.