While there are plenty of wireless temperature/humidity displays to choose from, getting the data out of them for our own home integrations is always a challenge. And while they're not always too expensive, things soon add up if you want them in every room. Throw in slightly more sophisticated sensing like PM2.5 or CO2 and the price skyrockets.   I have mentioned before how I use low-cost BTLE thermo-hygrometers with custom firmware to expose their data as BTLE beacons. Gathering the d