key fob vs keychain

key fob

noun
  • An item carried on a key ring either as decoration or security. 

  • A passive wireless electronic device that usually uses RFID technology to control access to buildings, containers, computers, etc. by being placed near a detector. 

  • An active wireless electronic device that controls access to buildings or vehicles, such as a remote control for a car door lock. 

keychain

noun
  • An ornamental piece holding such a chain or ring. 

  • A chain or ring to which a key may be attached. 

  • A digital repository for the storage of cryptographic keys. 

How often have the words key fob and keychain occurred in a corpus of books? (source: Google Ngram Viewer )