Synonyms and related words :
agile, alert, alive, astute, attentive, awake, aware, bright, clear-sighted, clear-witted, clearheaded, conscious, keen, nimble, on the, on the alert, on the ball, on the job, open-eyed, prompt, qui vive, quick, ready, sensible, sharp, sleepless, smart, unblinking, unnodding, unsleeping, unwinking, up, vigilant, wakeful, watchful