The abbreviation VOC stands for Volatile Organic Compunds and refers to a group of volatile organic components. The umbrella term VOC describes gaseous and vaporous substances of organic origin in the air. These include, for example, hydrocarbons, alcohols, aldehydes and organic acids. Since VOCs consist of several gases and vapors, their sources are also very different in nature. For example, VOCs in outdoor air are produced by biodegradation processes or substance combustion. Indoors, VOCs can vaporize from building materials, such as flooring, paint, furniture, adhesives, or cleaning materials. Inhalation of these gases and vapors can cause odor nuisance, irritation and, in extreme cases, carcinogenic, mutagenic and reproductive toxicity. To minimize these adverse health effects, VOCs are measured and controlled via special VOC transmitters.

VOC measurement is used where volatile organic components occur in borderline concentrations and can cause health effects. This explicitly applies to new buildings or renovations where gases and vapors can escape from building materials such as adhesives, carpets, floors or paints. There are no binding limit values for indoor areas, but the Federal Environment Agency gives reference and guideline values to serve as an orientation for indoor air quality and its contamination with volatile organic components. A VOC measurement can therefore be used in ventilation systems to form a further control variable for indoor air quality in addition to humidity, temperature and CO2 values.

Metal oxide sensors are used to measure volatile organic components. Metal oxide sensors consist of a heating element on which a film of metal oxide particles and two electrodes are deposited. Heating the heating element causes negatively charged oxygen species to react with gases in the ambient air, changing the electrical resistance of the metal oxide film. The change in resistance is detected by the integrated electronics and consequently allows conclusions to be drawn about the gas concentration in the air. The analog or digital output signals of the VOC transmitters allow the gas changes to be converted into a proportional electrical signal that can be used to control the ventilation system.