watchful

from The American Heritage® Dictionary of the English Language, 5th Edition.

• adjective Closely observant or alert; vigilant: synonym: careful.
• adjective Archaic Not sleeping; awake.

from The Century Dictionary.

• Wakeful; sleepless.
• Vigilant; careful; wary; cautious; observant; alert; on the watch: with of before the thing to be regulated or observed, and against before the thing to be avoided: as, to be watchful of one's behavior; to be watchful against the growth of vicious habits.
• Synonyms Watchful, Vigilant, Wakeful, attentive, heedful, circumspect, guarded. Wakeful refers to the lack of disposition to sleep, especially at times when one would ordinarily have such a disposition; watchful and vigilant refer to the mind, will, or conduct: they are of about equal vigor; watchful is the broader in its range of meaning.

from the GNU version of the Collaborative International Dictionary of English.

• adjective Full of watch; vigilant; attentive; careful to observe closely; observant; cautious; -- with of before the thing to be regulated or guarded; ; and with against before the thing to be avoided.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective observant, vigilant and aware

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• adjective engaged in or accustomed to close observation
• adjective experiencing or accompanied by sleeplessness