CO2 transmitters are available in different enclosures. These NDIR CO2 sensors measure temperature, relative humidity and CO2. Carbon dioxide or CO2 is a result of human metabolism. Moderate to high levels of CO2 can cause headaches and fatigue. To prevent or reduce high concentrations of carbon dioxide in a building or room, fresh air should be supplied to the room. NDIR is an industry term for “nondispersive infrared”, and is the most common and adequate type of sensor used to measure CO2.