Came here to say something similar. I expected an actual circuit build (of which there are many), but this is just plugging in a USB data logging CO2 monitor (which is $116 on Amazon right now, but apparently the normal price is ~$70 USD) and using it with Prometheus. I've done something similar wrapping https://github.com/merbanan/rtl_433 to pick up temp / humidity monitoring data from sensors around my home, then stuffing the results into InfluxDB and using Kapacitor for alerting (sends me an email when my freezer gets too hot) + Chronograf for graphing. It took an evening of reading docs and messing around to get it all working, and I'd recommend Ding I Y if it sounds cool -- you'll very likely learn something. Note that you could do the same with an ELK stack or Sensu or Nagios or whatever you want to play with.