Typically, these are classrooms, lecture halls, conference rooms, but also production facilities, open-plan offices, and generally event spaces. 1400 ppm of CO2 in the indoor air is already considered very poor air quality, while the maximum workplace concentration (MAK) in Germany is set at 5000 ppm. The GX-D2 alerts with a loud signal as soon as CO2 levels reach 2500 ppm, prompting thorough ventilation of the room. Those who have to breathe in consistently poor and stale air will become tired and significantly lose their performance and concentration abilities. This is particularly noticeable when learning and working. The immune system is also measurably weakened, which can be reflected in increased sick days in open-plan offices. The only remedy is regular cross-ventilation, which is often forgotten. This is where the GX-D2 warning device comes into play. It not only warns of elevated harmful concentrations but also encourages timely ventilation before the alarm sounds.