For everything non-Radon, I'd trust Awair (http://getawair.com) honestly. I feel like I'm shilling for them at this point. Outside of DHH's recommendation, I read somewhere that their sensors are certified (plus their 2nd Edition does PM2.5 and CO2, unlike the foobot one). I've looked into smart things, but I'm not concerned about Radon, so wasn't going to pay the extra $75.