Alert status

In the course of traveling in groups or large vehicles, an alert status is used by leaders of service and military organizations to communicate to all members of a unit when readiness for action is needed.

Starfleet
The Earth Starfleet began without an alert status system until one was suggested by Lieutenant Malcolm Reed aboard the prototype Enterprise, an early starship that had a larger crew and a greater need for reaction time during crisis situations. Lieutenant Reed's tactical alert utilized audio announcements, including a siren noise which was initially displeasing to other Enterprise personnel.

Starfleet alerts

 * battlestations
 * intruder alert
 * condition green
 * yellow alert (condition yellow)
 * red alert (condition red)
 * double red alert
 * blue alert
 * tactical alert