keenly watchful to detect danger; wary

a vigilant sentry.

ever awake and alert; sleeplessly watchful.

adjective

careless , impulsive , inattentive , indiscreet , negligent

adjective

acute , agog , alert , anxious , attentive , aware , cautious , circumspect , guarded , keen , looking for , looking to , observant , on alert , on guard , on the ball * , on the job , on the lookout , on the qui vive , on toes , open-eyed , sharp , sleepless , unsleeping , waiting on , wakeful , wary , wide-awake , with eyes peeled , with weather eye open , watchful , awake , careful , heedful , shrewd