Just to note that these require known-compatible Zigbee repeaters to stay connected (at least on all hubs before the C-8). I have 2 (and use Ikea outlets as repeaters) and they do work nicely.
@salieri, If you are looking for a standalone sensor with a display that also reports to the hub, I have one of these Thirdreality Zigbee temp & hum sensors with an LCD display. It uses 2 AA batteries and I hope that promises a long battery life.
I compared it to several other sensors I have and it gave similar readings, including the Aqara mentioned above -- you can see it in the pictures in my review:
