alert

(DOD, NATO) 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. To forewarn; to prepare for action. See also airborne alert. 5. (DOD only) A warning received by a unit or a headquarters which forewarns of an impending operational mission. 6. (DOD only) In aviation, an aircraft and aircrew that are placed in an increased state of readiness so that they may be airborne in a specified period of time after a launch order is received. See also air defense warning conditions; ground alert; warning order.