An evacuation alert, or evacuation alarm, was used to signal a mandatory evacuation of a certain deck, ship, planet, or starbase. It was normally used during a catastrophic event such as a hull breach or a loss of antimatter containment. This was a higher alert state than battle stations or red alert.
Aboard Enterprise NX-01, containers were available for emergency evac situations. (ENT: "The Catwalk")
In 2369, Lieutenant Commanders Data, Geordi La Forge, and Deanna Troi transported into the engine room of a Romulan ship where they found the ship's crew under evacuation alert. (TNG: "Timescape")
In 2371, Chief Miles O'Brien experienced a series of timeshifts into the future, one of which showed station Deep Space 9 put under evacuation alert prior to its destruction. (DS9: "Visionary")
During the failed Red Squad attack on a prototype Dominion warship, Nog triggered an evacuation alert from the USS Valiant's conn. (DS9: "Valiant")
After the Breen energy dissipator crippled the USS Defiant, Captain Sisko ordered an evacuation of the ship, triggering an evacuation alert. (DS9: "The Changing Face of Evil").