Key fobs were made as a decorative piece attached to the end of the key ring before it started appearing on American Motor vehicles in 1983. The term key fob was used to describe any small decorative token attached to a keychain.
Others have suggested that the term stands for frequency operated button, but that ignores heavy use of the word before the remote keyless entry system. They could represent a favorite sports team, cartoon character, etc. There were also key fobs that are far more useful which has items like bottle openers, small flashlights, and more.
Fobs are designed to lock/unlock cars, start the engine (Remote Keyless Ignition RKI), and open the trunk . These fobs can be purchased at car dealerships and automotive parts stores. RemotesAndKeys.com is one of the excellent resource for replacement remotes/fobs, which has remotes for all kinds of vehicles and finding a Great Deal. Today, the term key fob is most closely associated with the small devices used to gain entry into apartment buildings or commercial offices.