What is the meaning of alert?

noun

• Condition of heightened watchfulness or preparation for action.
  • usage: "bombers were put on alert during the crisis"
  • synonyms: qui vive
• A warning serves to make you more alert to danger.
  • synonyms: alerting
• An automatic signal (usually a sound) warning of danger.
  • synonyms: alarm, warning signal, alarum

verb

• Warn or arouse to a sense of danger or call to a state of preparedness.
  • usage: "The empty house alarmed him"; "We alerted the new neighbors to the high rate of burglaries"
  • synonyms: alarm

adjective

• Engaged in or accustomed to close observation.
  • usage: "caught by a couple of alert cops"; "alert enough to spot the opportunity when it came"; "constantly alert and vigilant, like a sentinel on duty"
  • synonyms: watchful
• Quick and energetic.
  • usage: "a brisk walk in the park"; "a lively gait"; "a merry chase"; "traveling at a rattling rate"; "a snappy pace"; "a spanking breeze"
  • synonyms: brisk, lively, merry, rattling, snappy, spanking, zippy
• (adj.) ().
  • synonyms: alive, awake