Land snails are perhaps best known for their slow speed and large shell they wear for protection against predators. Land snails are also problematic for gardeners since they will feast on lettuce, spinach and other leafy greens in the garden, and the constant damage could kill off the plant. Land snails also leave behind a trail of mucous as they slide, which is another source of irritation when they get near your home. Telling if a land snail is alive or dead requires simple observation.
Watch the snail for several minutes. If it doesn't move, it may be dead.
Poke the snail gently with a finger. Snails don't bite, and the snail will likely recoil or retreat into its shell upon your touching it if it is still alive.
Place the snail on the end of a flashlight and turn it on. You should be able to see the snail's heart beating through the shell if it is still alive.
Spray the snail with water from a spray bottle. If its conditions are too dry, the snail may have gone into a hibernation-like state called "estivation." Adding moisture may cause it to start showing signs of life.
Hold a lettuce leaf up to the snail to see if it tries to feed. If there has been no motion or response during any of these activities, the snail is likely dead.