radar vs smoke signal

radar

noun
  • A superior ability to detect something. 

  • A method of detecting distant objects and determining their position, velocity, or other characteristics by analysis of sent radio waves (usually microwaves) reflected from their surfaces 

  • A type of system using such a method, differentiated by platform, configuration, frequency, power, and other technical attributes. 

  • An installation of such a system or of the transmitting and receiving apparatus. 

verb
  • To scan with radar, or as if with radar. 

smoke signal

noun
  • A message or sign sent by this method. 

  • A method of long-distance communication sometimes used in ancient and undeveloped societies, consisting of messages conveyed by means of columns or intermittent puffs of smoke. 

  • An indirect message or indication, especially concerning a future event. 

  • A type of flare or combustion device sometimes used as a distress signal. 

How often have the words radar and smoke signal occurred in a corpus of books? (source: Google Ngram Viewer )