The TRILUX CO² sensor determines the CO² content in the air on the basis of photoacoustic spectroscopy (PAS). The reliable CO² measurement in combination with an integrated traffic light display enables intelligent monitoring of indoor air quality, so that users can improve the ambient conditions or air quality through targeted ventilation. A yellow or red traffic light display of the sensor warns of an excessive CO² and corresponding aerosol concentration, once the indoor air quality is restored, this is indicated by a green traffic light. Sensor is immediately ready for operation and maintenance-free, commissioning not necessary.