alertest
adjective
Quick to notice any unusual and potentially dangerous or difficult circumstances; vigilant.
an alert police officer discovered a lorry full of explosive
vigilant,wide awake,aware,watchful,attentive,observant,circumspect,wary,chary,heedful,canny
noun
The state of being watchful for possible danger.
security forces are on the alert for an upsurge in violence
vigilance,watchfulness,carefulness,attentiveness,guardedness,care,caution,cautiousness,wariness,chariness,alertness,circumspection,prudence,heedfulness,heed,mindfulness
verb
Warn (someone) of a danger or problem.
he alerted people to the dangers of smoking
warn,notify,apprise,caution,put on one’s guard,forewarn,put on the qui vive,arouse