1. Carefully observant or attentive; on the lookout for possible danger
   "there was a watchful dignity in the room"; "a watchful parent with a toddler in tow";
   - Argus-eyed, open-eyed, vigilant, wakeful
    
2. Engaged in or accustomed to close observation
   "caught by a couple of watchful cops";
   - alert
    
3. Without or unable to sleep
   "twenty watchful, weary, tedious nights";
   - insomniac, sleepless

See also: awake, fly [Brit, informal], full of life, heads-up, lidless [archaic], lively, sleepless, vital, wary, wide-awake

Encyclopedia: Watchful