VIGILANT

adj. watchful, alert, sharp, observant, guarded, circumspect, attentive, wakeful, cautious, careful, wary, chary, on one's guard, on the alert, on the lookout, eagle-eyed, hawk-eyed, Argus-eyed, on the qui vive, on one's toes, with one's eyes open, Colloq with one's eyes skinned or peeled As long as we remain vigilant, they will never be able to take us by surprise