Hey Community! I’m a long-time lurker and HA user. As winter season approaches quickly again, I have once again started looking into a CO2 Sensor that fulfills all my (nerdy) needs. Something simple, reliable, non-cloud, can generate statistics and can also output some form of status. Also many projects just come with some kind of cheap sensor that tries to estimate the CO2 value from other measurements… not really what I want 
Now hear me out on the display topic. I decided that I wanted something that is simple and does not include any traditional e-ink display, but rather a traffic light style with individual RGB LEDs. This is enough to display the current status and can also allow individual LEDs to be used for secondary information, but it doesn’t cost a fortune and is a much more “minimal” approach.
Now, couldn’t you just easily put all of that on a breadboard? Yes, you could! But wouldn’t it be much nicer if there was a device that you can simply flash through it’s USB type-c port?
For the sensors, I chose an SCD41 (high accuracy even for higher CO2 values) and a BME280, which allows us to provide pressure compensation data to the SCD41 locally. Additionally, I added an illuminance sensor that you could use to control the brightness of the 8 SK6812 LEDs. There is also a small buzzer that I personally won’t use but could become handy for some kind of CO2 “alarm” or just playing subtle notifications.
Now, please provide your thoughts including your views on sensors, LEDs vs. display, power etc! I currently run a prototype with the v1 prototype being ready shortly. Please note the “for ESPHome” is still pending!
Some sort of edit: I already sell electronics within the EU and now about the regulatory requirements. EMC testing will be performed and I plan to sell the PCB fully assembled as “product”.