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, to prevent drowning. Some modern lifebuoys are fitted with one or more seawater-activated lights, to aid rescue at night.
The lifebuoy usually is ring- or horseshoe-shaped and has a connecting line allowing the casualty to be pulled to the rescuer. They are carried by ships and are also located beside bodies of water that have the depth or potential to drown someone. They are often subjected to vandalism which, since the unavailability of lifebuoys could lead to death, may be punished by fines (up to £5,000 in the United Kingdom) or imprisonment.
The "kisby ring", or sometimes "Kisbie ring", is thought to be named after Thomas Kisbee (1792–1877) who was a British naval officer.
In the United States, Coast Guard approved lifebuoys are considered Type IV personal flotation devices. At least one Type IV PFD is required on all boats 16 feet or more in length, except canoes and kayaks.