vigilant

adjective

there had been a rash of petty thefts and we were warned to be vigilant:

watchful, on the lookout, observant, sharp-eyed, keen-eyed, gimlet-eyed, eagle-eyed, hawk-eyed, with eyes like a hawk, with one's eyes open, keeping one's eyes peeled/skinned, attentive, paying attention, alert, on the alert, on one's toes, on the qui vive;

awake, wide awake, unsleeping, on one's guard, on guard, concentrating, careful, cautious, wary, chary, circumspect, prudent, heedful, mindful;

prepared, ready;

informal beady-eyed, not missing a trick, on the ball, keeping a weather eye on things, leery;

rare regardful, Argus-eyed.

▷antonyms negligent, inattentive.

vigilant Oxford Dictionary of English