Sufficient ventilation and compliance with hygiene standards help to control the spread of infectious diseases. The SARS-CoV-2 industrial safety regulation points out that increased ventilation can effectively reduce the concentration of viruses in room air. 1,000 ppm of CO2 is a guide value from the German Technical Rules for Workplaces ASR A3.6.
The German Robert Koch Institute also writes that prolonged stays in poorly ventilated rooms increase the probability of infection by inhaling virus-contaminated aerosols.
Public authorities, retirement homes, church communities, unis, schools and kindergartens already use CO2 monitors to quickly determine whether the indoor air contains so much carbon dioxide that the room should be ventilated. PCE Instruments offers different easy-to-handle devices for CO2 measurement.
These air quality meters show the CO2 value and many models additionally show a colour coding which facilitates the evaluation of the air quality.
More information can be found here: https://www.pce-instruments.com/english/measuring-instruments/test-meters/carbon-dioxide-meter-kat_150849.htm