Just do reality-checks that can be done without moving at all. I have 3 reality-checks that I can do within 5 seconds, and nobody can see it. I have two ways of blocking the air-ways. I tested this reality-check in a lucid-dream once, and it works. I can clock the air-ways from inside, so I won't need any real physical movement. The other reality-check is to focuse on my nose with both eye opened. I can't see my nose this way in dreams either, so there.