Eventually this sort of thing will be triggered with gestures. Big at first, but gradually smaller until one can input surreptitiously.

Gestures from way across the room or from a separate room entirely? To me voice beats that.

I'm not sure why it should matter where one is when one performs a gesture. If I'm sitting on the couch I certainly don't want to have to stand up to adjust the lighting. Everything gets smaller until it eventually disappears, and the future versions of Echo etc. will just be integrated into the ceiling or a "smart" shirt or whatever. One won't have to worry about where they are, unless one wants to have a conversation without FBI or the spouse hearing it.