Instructions
Hold the snail up to a bright light. If the snail is young and the shell is translucent enough, you will be able to see its heart. A beating heart indicates a live snail. If you can't see the snail's body through the shell at all, it is most likely dead and decomposed.
Sniff the shell opening. A foul odor indicates a dead snail. A fresh odor indicates a living or very recently deceased snail.
Touch the "door" in the snail shell opening. If the door is closed tightly, the snail is alive. If the door is slack, the snail is dead -- when a snail dies, its muscles relax, and the door remains partially open.
How to Know When an Aquatic Snail Is Dead
When aquarium fish die, they stop moving and usually float to the surface of the tank. Live aquatic snails, on the other hand, may remain still for days at a time and float on the surface of the water when air fills up their lungs. Unfortunately, many pet parents, unable to tell whether their pets were alive, have buried or thrown away perfectly healthy snails. Depending on the snail's breed and the conditions of your tank, it may move nocturnally or only when feeding. If your snail is floating or stayed in its shell for days on end, you should inspect it before assuming the worst.