Red alert, also known as condition red or code red, was the highest alert signal status on Starfleet vessels and starbases.
A Galaxy-class alert indicator in normal, yellow alert, and red alert modes
One stage above a yellow alert, this status had weapons systems and shields brought to full power, essentially preparing the ship for combat. (Star Trek III: The Search for Spock) The Klingon equivalent of this status was defense condition one.
The Klingon equivalent for red alert may be a reference to the American alert system DEFCON.
Red alert could also be ordered during various other emergency situations, such as a ship being boarded, radiation exposure, a security alert, massive systems failure, an imminent warp core breach, and an evacuation order, among others.
A red alert could either be activated manually by the commanding officer or the officer in charge, or automatically, as when a ship was attacked, or entered a dangerous area, etc. The raising of shields automatically triggered a red alert. The ability to activate red alert could apparently also be granted even to non-ranking crewmen at discretion, as Seven of Nine had clearance to place the USS Voyager on red alert.
Sections of a starship could be placed on red alert while other sections remained at a lower alert status.
During a red alert, lights were dimmed, computer terminals showed constant red graphics, and alarms would sound.
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