listener vs watchdog

listener

noun
  • Someone who listens, especially to a speech or a broadcast. 

  • A musical anthology. 

  • A function that runs in response to an event; an event handler. 

  • A person's ear. 

watchdog

noun
  • An individual or group that monitors the activities of another entity (such as an individual, corporation, non-profit group, or governmental organization) on behalf of the public to ensure that entity does not behave illegally or unethically. 

  • A guard dog. 

verb
  • To perform a function analogous to that of a watchdog; to guard and warn. 

  • To be continuously reset by a watchdog timer. 

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