Synonyms for Alert:

adj.

all (adjective)
watchful.
attentive (adjective)
fascinated, regardful, attentive, absorbed, interested, cautious, entranced, responsible, observant, Hearkening, engrossed, observing, careful, Immersed, diligent, Concentrating, enraptured, sharp, watchful, concerned, mindful, Scrutinizing, rapt, heedful, intent, Considering, vigilant.
attentive, lively (adjective)
intelligent, bright, careful, clever, vigilant, wary, observant, active, heedful, sharp, wide-awake, circumspect, ready, watchful.
cautious (adjective)
wary, watchful, heedful, observant, careful, attentive, guarded, deliberate, prudent, circumspect, mindful, cautious, aware.
enthusiastic (adjective)
keen.
intelligent (adjective)
bright, clever, study at.
lively (adjective)
enthusiastic, lively, mettlesome, active, vigorous, vital, brisk, animated.
sharp (adjective)
sharp, quick-witted.
vigilant (adjective)
scrupulous, prepared, guarded, vigilant, meticulous, fastidious, attentive, open-eyed, diligent, mindful, watchful, precise, sharp-eyed, fussy, exacting, thoughtful, ready, heedful, observant, thorough, careful, conscientious, strict, prudent, finical, regardful, cautious, responsible, provident, particular.

n.

relay, report, tell, brief, give someone to understand (that), let someone know, divulge, deliver. early warning, code red, do's and don'ts, alarm bells, red alert, put on guard. awareness, well-adjusted, Compos-mentis, with-it, clear, clearly, thinking, lucid, sane. focused, under someone's critical eye, smart, fixated, quick-witted, keen, bright, attention span, clever, attention, Sharp-witted, regard, ability. tocsin, portend, sound/raise the alarm, warn off, lecture, tip off. alarm (noun)
flare, whistle, beacon, buoy, siren, semaphore, horn, foghorn, call, signal, bell.
alert (noun)
intelligent, vigilant, watchful, conscious, wakeful, alerting, aware, heads-up, fly, perked up, alarum, perked, qui vive, open-eyed, wide-awake, on the alert, warning signal, perched, alive, argus-eyed, alarm, lidless, sleepless, on-the-job.
communication (noun)
alerting.
indication (noun)
icon, logotype, key, denotation, indication, gesticulation, crest, lighthouse, marker, notation, legend, badge, pointer, figuration, symbol, sign, designation, emblem, guidepost, banner, insignia, logo, token, hint, signpost.
state (noun)
qui vive.
warning (noun)
sign, tip off, advisory, caveat, wink, threat, siren, signal, notice, warning, alarm.

v.

alarm (verb)
panic, scare, startle, dismay, surprise, frighten, shock.
caution (verb)
caution, enjoin, warn, admonish, Forewarn, advise, exhort.
communication (verb)
alarm.
indicate (verb)
label, wave, guide, note, mark, nudge, shrug, betoken, cue, gesticulate, indicate, gesture, beckon, stamp, point, brand, denote, point out, prompt, tag, notify, nod, ticket, wink, symbolize, flag, designate, motion.
warn (verb)
notify, flag, put on guard, Forewarn, alarm, threaten.

Other synonyms:

portend, warn off, attention, focused, early warning, Compos-mentis, well-adjusted, thinking, lucid, code red, attention span. sane, smart, tocsin, clearly, Sharp-witted, tip off, keen, clever. regard, lecture. clear. caution
exhort.
conscious
conscious.
on the job
on-the-job.
wakeful
wakeful.

Usage examples for alert

  1. Shirley Sumner's alert glance followed Bryce's as it swept around the room. – The Valley of the Giants by Peter B. Kyne
  2. Do you generally swing round in that alert manner when you hear somebody behind you? – The Coast of Adventure by Harold Bindloss
  3. Renfrew felt that she was suddenly alert – Bye-Ways by Robert Smythe Hichens