This is so fantastic. Trying to figure out where to put one in my house.
Birdie Tells You When It's Time to Open a Window for Fresh Air https://design-milk.com/birdie-tells-you-when-its-time-to-crack-open-a-window-for-fresh-air/?utm_source=rss&utm_medium=rss&utm_campaign=birdie-tells-you-when-its-time-to-crack-open-a-window-for-fresh-air
@AnnemarieBridy And the ideal sensor is easily obtainable. It even has its own temperature and humidity sensors as well. (Turns out it needs them to in order to produce an accurate CO2 reading, but you can tap them yourself as well.) So there's a couple of nerdy hours I can spend on another side project...