Thanks to @Brian_Linuxing for sharing on Twitter.
This German maker is helping schools make these CO2 monitors. Indoor CO2 measurements can reveal how well or poorly ventilated an indoor space is.
Here’s an interview with him in Make Magazine and a useful explainer video on CO2 in closed spaces, from The Verge.
I think we might want to make one of these for our indoor repair events. What does everybody think?
cc @Culture_of_Repair because of the link to schools
Looks interesting, got a couple of ESP8266 lying around I could start this with, but not sure where the cost estimate of 40 euros comes from, because I can’t find the CO2 sensor for less than £60-ish. Any cheaper source?
Check out @Brian_Linuxing’s original thread - he has a number of other maker projects. I recall Guido saying they accommodate something like three different sensors, knowing that there might be supply chain issues. Perhaps the price issue is, erm, recent to the Delta variant spreading 
https://twitter.com/BrianLinuxing/status/1428667580739379201
That’s more realistic pricing, although remains to be seen how good they are (prices from ebay including shipping):
Comments on that twit you linked to say avoid the cheap sensors because the SCD-30 (which is the £60-ish part I looked for first) measures CO2 properly rather than the cheaper sensors which deduce it from Voc levels… If I find the energy I might try decode whether that matters, but I’ll probably buy the two cheapest to try out.