alert

(noun) condition of heightened watchfulness or preparation for action. Synonyms: qui vive. Example: "Bombers were put on alert during the crisis."

(noun) a warning serves to make you more alert to danger. Synonyms: alerting.

(noun) 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. Synonyms: alarm. Examples: "The empty house alarmed him." "We alerted the new neighbors to the high rate of burglaries."

(adj) engaged in or accustomed to close observation. Synonyms: alert (vs. unalert), watchful. Examples: "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."

(adj) quick and energetic. Synonyms: brisk, lively, merry, rattling, snappy, spanking, zippy. Examples: "A brisk walk in the park." "A lively gait." "A merry chase." "Traveling at a rattling rate." "A snappy pace." "A spanking breeze."

(adj) mentally perceptive and responsive;"an alert mind". Synonyms: alive(predicate), awake(predicate). Examples: "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."