A key fob is a decorative item which many people carry with their keys, on a ring or a chain, often to provide a better grip or to simply make a personal statement. There is essentially no limit to the forms of key fobs available. Simple shapes of smooth metal or plastic, often with a message or symbol, are the most common. Some may be shaped into symbols or small representations of objects, or may be functional in themselves – small flashlights, calculators, penknives or other items are common. See keychain for a more extensive list of such items.

A Key FOB is a type of security token: a small hardware device with built-in authentication mechanisms. Just as the keys held on an ordinary real-world key chain or fob control access to the owner's home or car, the mechanisms in the key fob control access to network services and information.