The CO2 Traffic Light will help to vent rooms at school, home, work to keep the aerosol concentrations low. We recommend to set the red light alert "must ventilate, open windows and doors" at 800ppm CO2. max 1000ppm. Follow your local government regulations. CO2 monitors are just a indicator for air quality, it will no protect you against virus or anything else. If you are not sure check resources on the principal of CO2 in breathing air and CO2 traffic lights in general. This is not meant to be a healthcare device or like. See this a foundation for STEM projects to work with sensor, IoT and learn about aerosols and CO2 impacting air quality indoors.
An interesting link found among my daily reading