What does "watchman" mean?

Watchman: Specifically, one who guards a building, or the streets of a city, by night. Watchman beetle (Zoöl.), the European dor. -- Watchman's clock, a watchman's detector in which the apparatus for recording the times of visiting several stations is contained within a single clock. -- Watchman's detector, or Watchman's time detector, an apparatus for recording the time when a watchman visits a station on his rounds. -- Watchman's rattle, an instrument having at the end of a handle a revolving arm, which, by the action of a strong spring upon cogs, produces, when in motion, a loud, harsh, rattling sound.