A yellow alert or condition yellow was the second highest alert signal status on Starfleet vessels, one stage below red alert. It designated a ship-wide state of increased preparedness for possible crisis situations.
In this status, a ship's defense fields were energized, and/or the deflector shields were brought to full power, but the weapons systems remained off-line. (TOS: "A Taste of Armageddon"; "The Lights of Zetar"; Star Trek II: The Wrath of Khan, Star Trek IV: The Voyage Home) Depending on the situation, the captain could order a reduction in the closing speed between itself and any potential incoming threats. (TAS: "The Pirates of Orion"; Star Trek IV: The Voyage Home)
A yellow alert could either be activated manually by the commanding officer in preparation for a tactical or environmentally hazardous situation, or automatically upon detection of unknown or hostile spacecraft, or upon detection of certain system malfunctions. If the situation escalated, the commanding officer or the main computer would order a red alert. (TNG: "Yesterday's Enterprise")
Yellow alert was not typically ordered in the Earth Spacedock, however, in 2285, such an order was given aboard the USS Excelsior when Admiral James T. Kirk was stealing the USS Enterprise. (Star Trek III: The Search for Spock)
In early 2365, when the USS Enterprise-D was approaching a void in space, Lieutenant Worf recommended that the ship go to yellow alert. When pressed by Captain Jean-Luc Picard for this recommendation, Worf responded that he was thinking about an old Klingon legend about a large space beast that devoured entire ships when he gave the recommendation. (TNG: "Where Silence Has Lease")
|Colored alerts:||Red • Double Red • Yellow • Blue • Gray|
|General alerts:||Battle stations • "Brace for impact" • General quarters|
|Battle • Evacuation • Fire • Intruder • Perimeter • Proximity • Security • Standby • Tactical|