watchful
watch-ful
adjective
Keeping careful observation; alert and vigilant, often for danger or opportunity.
"The security guard remained watchful throughout the night."
Thesaurus
Synonyms: wakeful, alert, vigilant, open-eyed, argus-eyed, sleepless, lidless, wide-awake, fly, heads-up, awake, insomniac
Antonyms: unalert, unvigilant, unwatchful