red alert

American  

noun

1. (in military or civilian defense) the most urgent form of alert, signaling that an enemy attack is believed to be imminent.

2. the signal or alarm sounded for this alert.

3. a signal or warning that a critical situation is developing or has occurred.

4. the period during which a state of crisis or danger is declared to exist.

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Etymology

Origin of red alert

First recorded in 1960–65

Example Sentences

France's national weather service had issued a red alert for avalanche risk for the area on Thursday.

From BBC

The army has been deployed to help with evacuations amid a red alert for more heavy rainfall this week.

From BBC

Mozambique has declared a red alert in the wake of the devastating floods while South Africa has announced a national disaster.

From BBC

Understandably therefore, the officials are on red alert, desperate to ensure any dangerous tackles or collisions don't slip through the net.

From BBC

Mexico put out a global Interpol “red alert” seeking Zhang’s capture.

From The Wall Street Journal