alert

alert someone

to something to make someone aware of trouble or potential trouble. The auditors alerted us to some problems with the accounts.

on the alert (for someone or something)

watchful and attentive for someone or something. Be on the alert for pickpockets. You should be on the alert when you cross the street in heavy traffic.

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be on full/red alert

if soldiers are on full alert, they know that a situation is dangerous and are prepared to act immediately if necessary The British flagship in the area went to battle stations and remained on full alert for twenty minutes.

See also: full