noun (n)

• the process of paying close and continuous attention(noun.cognition)

  Synonym:
  vigilance, wakefulness, watchfulness
  

  source: wordnet30
• a state of readiness to respond(noun.state)

  Synonym:
  alerting
  

  source: wordnet30
• lively attentiveness(noun.attribute)

  Synonym:
  on the qui vive, sharp-sightedness
  

  source: wordnet30
• The quality of being alert or on the alert; briskness; nimbleness; activity.(noun)

  source: webster1913