ASHRAE's definition of acceptable indoor air quality demands air in which there are no known contaminants at harmful concentrations and air with which a substantial majority (usually 80 %) of the people exposed do not express dissatisfaction. Investigations on indoor air pollutants and emission sources are the scientific way to a good indoor air quality tomorrow. To guarantee pleasant and healthy breathing indoors today the control of IAQ is necessary. Demand ventilation control by unspecific sensors is one possible way there.