Today a life jacket is called a personal flotation device (PFD), life preserver, life belt, cork jacket and various other names. Contemporary flotation devices in the form of a vest are fastened to the person to prevent the individual from drowning in a body of water. As designed, the person is kept afloat with his/her head and mouth above the surface of the water so that they can breathe and tread water and don’t have to swim. The person could even be unconscious and remain afloat.

Primitive life jackets can be traced back to inflated bladders, animal skins, or hollowed-out gourds for support when crossing deep streams and rivers. Later, buoyant safety devices consisting of simple blocks of wood or cork were used by Norwegian seamen.

By the early 1800s, a cork life jacket was available for sale in ‘The Sporting Magazine’.

Personal flotation devices were not part of the equipment issued to naval sailors until the early 19th century. For example, at the Napoleonic Battle of Trafalgar (1805), seamen who were forced into naval service might have used such devices to jump ship and swim to freedom.

In 1900, French electrical engineer Gustavo Trouve (1839-1902), patented a battery-powered wearable life jacket. It incorporated small, rubber-insulated maritime electric batteries not only to inflate the jacket, but also to power a light to transmit and receive SOS messages (Morse code distress signal) and to launch a distress flare.

More Info: en.m.wikipedia.org