Čo je alert? Čo je alert? Vigilantly attentive; watchful: alert to danger; an alert bank guard. See Synonyms at aware.Mentally responsive and perceptive; quick.Brisk or lively in action: the bird's alert hopping from branch to branch. A signal that warns of attack or danger: Sirens sounded the alert for an air raid. A condition or period of heightened watchfulness or preparation for action: Nuclear-armed bombers were put on alert during the crisis. To notify of approaching danger or action; warn: a flashing red light that alerted motorists to trouble ahead. on the alert Watchful and prepared for danger, emergency, or opportunity: bird watchers on the alert for a rare species.