S: (v) alarm, alert (warn or arouse to a sense of danger or call to a state of preparedness) "The empty house alarmed him"; "We alerted the new neighbors to the high rate of burglaries"
Adjective
S: (adj) alert, watchful (engaged in or accustomed to close observation) "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"
S: (adj) alert, brisk, lively, merry, rattling, snappy, spanking, zippy (quick and energetic) "a brisk walk in the park"; "a lively gait"; "a merry chase"; "traveling at a rattling rate"; "a snappy pace"; "a spanking breeze"
S: (adj) alert, alive, awake (mentally perceptive and responsive) "an alert mind"; "alert to the problems"; "alive to what is going on"; "awake to the dangers of her situation"; "was now awake to the reality of his predicament"