(1) A remote control car door opener such as the common "clicker" used with most modern automobiles.
(2) A USB flash drive used for storage or as an identification key. See
USB drive and
authentication token.
(3) A security token that is attached to a keychain. Ironically, the word is also used as the antithesis of security: "fob off" means to "palm off" a shoddy trinket through deception. See
authentication token.