alert
a-lert
adjective
Watchful and ready for danger or quick perception.
"The guard remained alert throughout his shift."
verb
To warn someone of danger, an emergency, or an attack.
"The system alerts users to suspicious activity."
noun
A state of readiness for potential danger or action.
"Troops were placed on high alert."
noun
A warning of danger, an emergency, or an attack.
"The weather service issued a flood alert."
Thesaurus
Synonyms: alerting, alarm, warning signal, alarum, argus-eyed, sleepless, lidless, wakeful, wide-awake, fly, vigilant, open-eyed
Antonyms: unalert, unvigilant, unwatchful