I’ve built a eCO2, humidity & temperature sensor.
Inspiration is from http://lafabrique.centralesupelec.fr/projetco2/ project, to help ventilate classrooms when eCO2 is too high (and so, indirectly can help to limit COVID-19).It uses an esp8266, a SGP30 eCO2 sensor and a DHT11 for humidity & temperature.
A high CO2 concentration means you should ventilate the room (and so, indirectly can help to limit COVID-19 indoors).
SPG30 doesn’t detect CO2 but can make a « equivalent CO2 » (not great but sensor is cheap, about 10 €).
It displays value on an OLED screen but can also send metric to an influxdb database, and be displayed on a grafana dashboard.
You can find the [code on github](https://github.com/paulgreg/co2-sensor).