1. Warn or arouse to a sense of danger or call to a state of preparedness
   "We alerted the new neighbours to the high rate of burglaries";
   - alarm

1. Engaged in or accustomed to close observation
   "alert enough to spot the opportunity when it came"; "constantly alert and vigilant, like a sentinel on duty"; "caught by a couple of alert cops";
   - watchful
    
2. Quick and energetic
   "The alert guard spotted the intruder immediately";
   - brisk, lively, merry, rattling, snappy [informal], spanking [informal], zippy [informal]
    
3. Mentally perceptive and responsive
   "an alert mind"; "alert to the problems";
   - alive, awake, on the ball

1. Condition of heightened watchfulness or preparation for action
   "bombers were put on alert during the crisis";
   - qui vive
    
2. A warning that serves to make you aware of danger
   "The tsunami alert prompted immediate evacuation of coastal areas";
   - alerting
    
3. An automatic signal (usually a sound) warning of danger
   "The fire alert sounded throughout the building";
   - alarm, warning signal, alarum [archaic]

Derived forms: alerts, alerting, alertest, alerter, alerted

See also: Argus-eyed, awake, aware, cognisant [Brit], cognizant, energetic, fly [Brit, informal], full of life, heads-up, lidless [archaic], lively, open-eyed, sleepless, vigilant, vital, wakeful, wary, watchful, wide-awake

Type of: preparation, preparedness, readiness, sign, signal, signaling [N. Amer], signalling [Brit, Cdn], warn, warning

Antonym: unalert

Encyclopedia: Alert, Nunavut, CA