Found 2 items, similar to on the alert.
English → English (WordNet) Definition: on the alert on the alert adj : watchful and prepared for action; “bird watchers on the alert for a rare species”; “cops were on the job and caught them red-handed” [syn: on the alert(p), on the job(p) ]
English → English (gcide) Definition: On the alert Alert \A*lert"\, n. (Mil.) An alarm from a real or threatened attack; a sudden attack; also, a bugle sound to give warning. “We have had an alert.” --Farrow. [1913 Webster] On the alert, on the lookout or watch against attack or danger; ready to act. [1913 Webster]