How can you tell if a hermit crab is dead or alive?

Usually to see if its dead, you smell the tank its in. If the smell is gross and very overwhelming, most likely its dead. If it only has a slightly fishy smell, its probably fine.

* Lots of times people confuse molting with death. Be sure your hermit crab isn't just molting before you get rid of it. * if you think your hermie may be dead, GENTLY shake the shell or GENTLY blow into it , the hermie may fall out. but make sure tis not just molting. My hermit crabs Shelly and Howard haven't moved for 3 weeks now, but I do know that usually when they molt they burrow under the sand or any other earth material you have. But since my hermit crabs haven't moved and haven't burrowed then it's time to dip them in the water and see if they're alive. * No one likes it when their crab dies. But when the crab gets too old it will just die. Since hermit crabs are nocturnal they usually die overnight. The hermit crab might start digging a hole in the sand or will stay on the top layer. (If they die underground you will want to dig it up, or else it will start to stink.) When your crab dies it will stink like fish for many days. Then you will have to remove it from its tank.