Do you already have/use a Hue bridge? If so, you can either pair it to that (and then bring it into HE from there - I use and recommend Robert's own CoCoHue app), or you can pair direct to HE.
There could be advantages either way... My outdoor sensor is paired to my Hue bridge because it primarily controls a Hue outdoor light, and I simply prefer to manage all that from my Hue bridge (long story).
But I have 2 other Hue indoor sensors that I've paired direct to HE. and those work great too.
