VERBS be, look, seem | become | remain, stay | keep sb The machine should help to keep the pilot alert.
ADV. very | fully | immediately, instantly, suddenly There was a noise outside and he was suddenly alert. | always, constantly | mentally He was as mentally alert as a man half his age.
PREP. to Climbers need to be alert to possible dangers.
ADJ. red His sudden disappearance triggered a red alert among his friends. | nationwide | bomb, fire, flood, pollution, security A security alert was issued after four men escaped from the prison.
VERB + ALERT issue, put out, raise, sound They rang the church bells to sound the alert and the villagers then fled. | spark, trigger | call off The alert was called off when it was found that the bomb was not live.
ALERT + VERB go out A nationwide alert went out for three escaped prisoners.
PREP. on the ~ | ~ for You should always be on the alert for anyone who looks suspicious.
PHRASES be on full alert The security forces are now on full alert. | keep/put/place sb on full alert Thousands of police were put on full alert at all main roads leading to the city. | a state of alert The army was yesterday placed on a state of alert in case of more riots.