Thanks, everyone! That's really helpful.
I too have several of my sensors on side tables and office desks and night stands, and such. That seems to work reasonably well as far as sensing the temperature. But they get picked up by people, and knocked on the floor, and just generally speaking, I think they should really be out of the way.
I would just like to attach them to something where people can't see it and be done with it. The ceiling would be the most convenient for that. (Note: I actually have several temperature sensors that are just temperature sensors). But then of course, that is going to be the warmest spot in the room, which is less than ideal, obviously. I have also considered places like window sills, but surely that isn't ideal either. So just on the wall? Hmmm... It's a conundrum.