Synonyms for Watchful (same or very similar meaning)
WordNet sense 1 (experiencing or accompanied by sleeplessness):
insomniac, sleeplessWordNet sense 2 (carefully observant or attentive; on the lookout for possible danger):
open-eyed, vigilant, wakeful, argus-eyedWordNet sense 3 (very attentive or observant):
alertFrom the ODE community, based on WordNetadd/edit