I've got a Qingping Air Monitor Lite - it's small, not ugly, and from what I read at the time, has a decent CO2 sensor. It integrates perfectly with Home Assistant via Bluetooth. Seriously, no issues once I got it setup - which I believe did require their app to do initial setup/updates/etc... https://www.home-assistant.io/integrations/qingping/ https://www.amazon.ca/Qingping-Monitor-Compatible-Temperature-Humidity/dp/B092HK4BB1