vigilant

Adjective

• carefully observant or attentive; on the lookout for possible danger
  • a policy of open-eyed awareness
    
  • the vigilant eye of the town watch
    
  • there was a watchful dignity in the room
    
  • a watchful parent with a toddler in tow
    

Related words

• Synonyms: 
  argus-eyed , open-eyed , wakeful