adjective
[more ~; most ~] :able to think clearly and to notice things
noun
plural alerts
[count] :something (such as a message or loud sound) that tells people there is some danger or problem :an alarm or signal of danger
[noncount] :the state of being ready for something you have been warned about (such as an attack) - used with on
on the alert
looking for or expecting something (such as danger or an opportunity)
verb
alerts; alerted; alerting
[+ obj] to give (someone) important information about a possible problem, danger, etc. :to warn (someone)
to make (someone) aware of something