A sensor for gases emitted by combustion, the sensor involving one or more metal oxides forming an adsorption semiconductor the electrical resistance of which changes according to the gas adsorbed, the semiconductor being a semiconductor for the direct adsorption of gases without catalyzed chemical reaction, the sensor being arranged to detect nitrogen oxides in the case of a bright fire, and/or the sensor being arranged to detect, in the case of a smoldering fire, partially unburned gases, in particular alcohols, aldehydes, ketones, carboxylic acids or amines.