Alert signal
Aboard Starfleet vessels and outposts, a series of color-coded alert signals were issued, usually by the ship's computer or internal communications systems.

The Earth Starfleet began without an alert status system (signal) 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.

While planning an escape from their hostage situation, Sub-Commander T'Pol mentioned that the sound of the transporter would alert the guards. ()

Colored alerts 
 Red alert (condition red) – critical situation, denoted by flashing red warning lights and audio alarms.
 Double red alert
 Yellow alert (condition yellow) – elevated alert
 Blue alert (condition blue) – environmental, docking/separation, or landing alert
 Gray mode
 Black alert
 Green alert

General alerts 

 Abandon Ship Klaxon
 Alert status four
 Battle alert
 Battle stations
 "Brace for impact"
 Emergency stations
 Evacuation alert
 Fire alert
 General quarters
 Intruder alert
 Perimeter alert
 Proximity alert
 Security alert
 Standby alert
 Tactical alert

de:Alarm
fr:Signal d'alerte
Alerts