WordReference Random House Unabridged Dictionary of American English © 2025
red′ alert′, 
            - (in military or civilian defense) the most urgent form of alert, signaling that an enemy attack is believed to be imminent.
 - the signal or alarm sounded for this alert. Cf. blue alert, white alert, yellow alert.
 - a signal or warning that a critical situation is developing or has occurred.
 - the period during which a state of crisis or danger is declared to exist.
 - 1960–65
 
'red alert' also found in these entries (note: many are not synonyms or translations):