The hardware itself is really simple. It uses a Nordic nrf51822 BLE SoC and is paired with the Sensirion SHT21 temperature sensor. The rest are just some standard capacitors, inductors and similar stuff. It doesn't use any premade hardware modules or anything like that. The whole RF side is done on this board itself. All of the components can be soldered together at home without any special tools (besides a temperature controlled soldering iron and some flux). Although I do recommend a hot air gun. But do note that small 0402 sized components are used, so you will need some practice.
More detailed instructions and all of the needed files (including gerbers, BOM, firmware hex, ...) can be found over on Github .