After having them for a while, you start to notice subtle signs of them being awake or asleep. Or at least, I can tell with a few of my snakes that are in tanks. It's difficult to explain, but they tend to lift their heads just a little bit when they're awake, and are usually fully relaxed when asleep. Ball pythons also tend to lean a little bit on their sides while sleeping, so you see part of their belly.

With those in the rack, they generally are woken by the motion of the bin being pulled out.