alert

n. 1. readiness for action, defense, or protection.

2. a warning signal of a real or threatened danger, such as an air attack.

3. the period of time during which troops stand by in response to an alarm.

4. a warning, received by a unit or a headquarters, that forewarns of an impending operational mission.

forewarn; prepare for action.

See the Introduction, Abbreviations and Pronunciation for further details.