This sounds like the first time you've had a hermit so here's a heads up:
If one day you look in your tank and you see that the shell is empty then look farther and see what looks like a dead crab in your tank, relax. It probably just molted (shed its "skin") and is hiding for protection till its new "skin" hardens. At which time it'll move back into its home.
But, every time it molts it grows so when it does, start planning on getting some empty shells of the same style and various sizes so it can eventually move to a bigger home.