The room air quality sensor serves for the requirement-dependant ventilation of living spaces, office premises, meeting rooms, hotels or restaurants. It serves for the quantitative evaluation of the pollution of the air in rooms with gases, such as used up breathing air, tobacco some, solvent vapours, cleaning agents and car fumes. The room air sensed by the sensor is being transduced to an output signal of 0-10 V or 4-20 mA. A minimal value at the output is interpreted as clean air, while a maximum value is valuated as strongly polluted air. The version with additional switching output has been present ex factory to a value that corresponds to 70 % of the maximum output value. This value can be adapted internally to the individually prevailing room occupancy and/or utilisation conditions. This air quality sensor is not suited for the execution of a selective CO2 measurement.