alertness

noun

The condition of being alert: vigilance, wakefulness, wariness, watchfulness. See awareness/unawareness.

Awareness of environmental stimuli and the ability to respond quickly to those stimuli. Alertness is reflected by an increase in electrical activity of the reticular formation and cerebral cortex in the brain.

The noun has 3 meanings:

Meaning #1: the process of paying close and continuous attention
  Synonyms: watchfulness, vigilance

Meaning #2: a state of readiness to respond
  Synonym: alerting

Meaning #3: lively attentiveness
  Synonym: on the qui vive