Wireless connection between indoor and outdoor sensors. Extended range of 100 m / 300 ft (without obstacles). 1 x Indoor module. 1 x Outdoor module. Min and max temperature, "feel like" temperature and dew point.
Works good. Bad part is that it does not show the actual CO2, but rather "Over the limit level" so if you air is always good you will not get precise measurement on how good it is, the device will show 0.
API and IFTTT integrations work great