radar vs watchtower

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. 

watchtower

noun
  • An observation tower in which a lookout keeps watch over prisoners, or looks out for fires, etc. 

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