lifebuoy

A lifebuoy, ring buoy, lifering, lifesaver, life donut, life preserver or lifebelt, also known as a "kisby ring" or "perry buoy", is a life saving buoy designed to be thrown to a person in the water, to provide buoyancy and prevent drowning. Some modern lifebuoys are fitted with one or more seawater-activated lights, to aid rescue at night.