I would not really recommend buying one of these sensors. But if you have one already, the custom firmware provided here is great to start tinkering with these boards.
Xiaomi Digital Hygrometer / Temperature and Humidity Monitor (with LCD screen)
Qinping / ClearGrass Temperature and Humidity Monitor (with EInk screen)
Xiaomi Digital Hygrometer 2 (LCD)
Xiaomi Digital Hygrometer 2 (EInk)
Xiaomi Digital Hygrometer Clock
Let's add more sensors!
WatchFlower has been built to be easily extensible, and compatible with as many Bluetooth sensors as possible.
If you develop a Bluetooth Low Energy device or know a good one, contact me, I might just add support for it!
WatchFlower is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the
Free Software Foundation; either version 3 of the License, or (at your
option) any later version.