GTrusted

Got this at the same time as the Elgato Eve Door & window sensor, and I have to say it works great. As with the Door & motion sensor, there's a bit of a lag, but this is due to be sorted in an upcoming software update, so it can only get even better, and I'm happy now.

Its quite compact, although not as small as the Hue motion sensor, but then that's not HomeKit compatible, so it won me over for that alone. Not a bad price either, and with low energy bluetooth, the battery lasts for a long time.