As the local proposal mentioned below was inspired by way too many hours on the birdsite, I must reference some very good folks there:

Delighted to report good #IAQ at Knox County #Public #Library @knoxreads@twitter.com! Sampled on 3 floors over an hour today -- #CO2 stayed under 800ppm! Even in a meeting room of 11 people across 45 minutes, #Aranet4 and #CO2Click showed < 800.

Really hoping #CO2monitor LENDING PROGRAM can be offered here! Thx for inspiration @CAVI_CO2@twitter.com,
@safe_breathe@twitter.com, &
@smarterHEPA@twitter.com

@czarbucks
Yes! Since about May. Use #CO2Click and #Aranet4HOME and got living room levels down to 600 to 700 pretty easily with a small window opening in dining room; bedroom down to 700 rather than 1100 in the morning, same solution. Finding lower levels now in colder weather; closing window to see what happens. Take one pretty much everywhere. My vet's exam room was over 2000ppm in Sept. 😵‍💫
Do you know about www.CO2trackers.com? Maybe you can add your data?

Sometimes you do have to recalibrate #Aranet4HOME. This one is about 3 months old, and after several hours outside, it hovered above 500 ppm. Should be ~420 to 440. Recalibrated and all is well. My #CO2Click and the Aranet4 are getting along quite well now.
Can't wait to compare both to the DIY #AirGradient arriving soon...

@DrOrna
Cost is the biggest con for #Aranet4. I wish it had date/time display. #CO2Click is about USD 175 and shown to be reliable; must charge at least once a day. Its maker, Canadian Andre Courchesne [@IndianaTux], continues to update firmware & cloud portal; terrific for customer service.
I'm awaiting arrival of Thai Air Gradient DIY kit to compare to both. Looks very promising, with Senseair S8 CO2 sensor (NDIR) & Plantower PMS5003 PM sensor!

@morganarae
Hope your vet's office has MUCH better air circulation / filtration than did mine in Sept. for new adopted kitty exam. #co2 well over 2000ppm with me masked and 3 other humans unmasked in small exam room. Lobby still over 1400ppm. #CO2Click monitor.
Really hoping not to need vet for new kitty til, IDK, 2024?
Vet declined my offer of specially made #CorsiRosenthalBox 😔

Curious who has used / is using a #CO2monitor such as the #Aranet4 or #CO2Click? Ambivalent about #Vitalight. Oh sure, I know #covid is over and everything with only 1000 deaths in 1 day reported across about half of the US states (/s). Seems it would be such an excellent #publichealth move to have #CO2 levels readily displayed so folks could make a more informed #riskAssessment.