watchful

adj. 1 accustomed to watching, alert. 2 on the watch.  watchfully adv. Watchfulness n.

a. Full of watch; vigilant; attentive; careful to observe closely; observant; cautious; -- with of before the thing to be regulated or guarded; as, to be watchful of one's behavior; and with against before the thing to be avoided; as, to be watchful against the growth of vicious habits.