If you want something that looks attractive in your room and has an app to view history (so the opposite of "hacker"), I highly recommend Awair, been using it f

If you want something that looks attractive in your room and has an app to view history (so the opposite of "hacker"), I highly recommend Awair, been using it for years: https://www.getawair.com/products/element https://www.getawair.com/products/element You can configure the device display to just show numerical CO2 (that's what I do). Seeing the CO2 history graphed on your phone might not seem like it's all that necessary, but I find it really is -- you can see how it falls when you're out, you can see how quickly it skyrockets when you turn on the oven, you can see how long it takes to settle into a steady state overnight. Seeing CO2 over time gives me a conceptual understanding of what's actually happening, which I didn't have with my previous CO2 monitor that just showed the current value.