fire alarm vs heads-up

fire alarm

noun
  • The sound or other warning made by a fire alarm. 

  • An electromechanical or electronic bell, klaxon, chime, horn, speaker, strobe light or other device which warns people in a building of a possible fire or other condition requiring evacuation. 

  • An emergency response to a fire by the fire department with manpower and equipment. 

heads-up

noun
  • A warning or call to pay attention; an advisory notice; a notice of what is to happen; a holler. 

  • Involving two players. (usually said when there are only two players in the table; or, when all players except two folded) 

adj
  • With head directly above the neck, eyes front. 

  • Alert; vigilant 

How often have the words fire alarm and heads-up occurred in a corpus of books? (source: Google Ngram Viewer )