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

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

From BBC

Mozambique has already been battling severe flooding in recent days, and the government has declared a state of "red alert" to expedite operations to tackle Freddy.

From Reuters

Federal health officials placed Mexico City on red alert Friday, a level determined by case loads, hospital bed availability and the rate of change in those and others factors.

From Seattle Times

The same public voices who have been sounding the red alert about Trump's neofascist movement and its escalating threat to democracy continued to do so.

From Salon

The weather department has issued a red alert, warning people of heavy rains over the next 24 hours.

From BBC