The 16th century saw the development of the pocket watch for members of the aristocracy. From their inception they were an item of expense and a status symbol. The pocket watch held its position until the start of WWI when watches with wristbands begin to find their way into trench warfare. Ironically, up until this time a watch with a band was considered a feminine style. Its adoption by soldiers changed the cultural assumptions of the style and the wristband watch replaced the pocket watch in popularity, with the wristwatch also falling out of popularity with the advent of the smartphone.
A pocket watch in contemporary society is either an item of eccentricity, or a strictly stylistic approach to an outfit. It no longer has any effective utility (at one time trains were run on the strict manufacturing requirements of the railroad pocket watch) and now as an accessory. The pocket watch holds the same territory as the pocket square, and item to give an outfit a certain punch. This transition from tool to knickknack gives the wearer a greater range in pocket watch style for what is now no longer useful need not conform to rules of fashion.
Traditionally, pocket watches were worn in a small pocket in the vest of a suit. They would be held to the vest with a chain. A pocket watch has essentially two parts, the watch case the watch movement. The watch movement is the internal gears which form the function of time keeping. The watch case is the casing that holds the mechanisms in place, including the crystal that covers the dial. The case merges with the hands and the hands are often considered part of the case.
The two basic styles of pocket watches are the open case and the hunter case. The open case is the style we usually picture. The open case lacks a metal cover to protect the dial and crystal. These watches are meant for more urban, structured spaces. Cases are made from a multitude of metals and the particular make of casing, whether gold or brass etc, depends on the wearer. Pocket watches also come in demi-hunter styles whereby a portion of the metal lid is cut out and allows the wearer to view a portion of the hands.
Though pocket watches are not out of fashion there are still companies making new designs. Recent trends are moving towards expensive military grade square models with a sleek futuristic design. These watches are likely to catch on with the general public and are cost prohibitive.