Tactical alert
Tactical alert was a security protocol instituted by Malcolm Reed in 2152 while under the influence of dangerous mind-affecting radiation aboard , in response to the perceived number of threats that were being encountered by the starship in their deep space exploration mission. The protocol was kept due to its usefulness. It was a precursor to the color-coded alert system used on later Starfleet vessels.

The alert was designed to automatically bring the ship to battle-ready status when a pre-programmed set of circumstances occurred (for instance, an impact to the hull, or an order from the captain). When a tactical alert was initiated, the hull plating was polarized, the weapons were automatically charged, and critical systems such as the warp core were secured. In addition, all crewmembers would report to battle stations upon initiation of the alert. The tactical alert was initially accompanied by a loud, grating klaxon, which aggravated Captain Jonathan Archer and Commander Tucker, who felt it sounded like "a bag full of cats." The klaxon was not retained in future uses of the alert. While in the process of naming the new condition, the terms "security protocol" and "condition red" were suggested. The term "Reed alert" was sarcastically suggested by Commander Tucker as a name while Lieutenant Reed was working on it, but was later dismissed by Reed as being "a bit narcissistic," whereas security protocol was deemed "not very dynamic." ()

By the 23rd century, tactical alert was replaced in Starfleet by the red, yellow, and blue alert conditions. (, et al.) 

This aside, the  utilized a form of tactical alert during its time in the Delta Quadrant in the 2370s. (, et al.)

It was also an alert status aboard Klingon Defense Force ships to indicate approaching hostile vessels. It was used on the IKS Rotarran during their mission to find and rescue the IKS B'Moth battle cruiser when the Rotarran's sensors detected a Jem'Hadar warship approaching their position near the Cardassian border. ()

The Pralor Automated Personnel Units utilized a tactical alert status aboard their vessels during the 2370s. ()

In an alternate timeline where Chakotay and Harry Kim attempted to alter history in 2390, the s computer signaled a tactical alert when the  approached to apprehend them. ()

Notable uses 
 Enterprise NX-01
 2153 – Captain Archer ordered tactical alert when Enterprise was searching the Borg-assimilated transport Arctic One. ()
 2154 – Lieutenant Reed ordered tactical alert when a Xindi-Insectoid starship opened a subspace vortex off the port  of Enterprise. ()
 2154 – Commander Tucker ordered tactical alert when Vulcan starships tried to force Enterprise from orbit of . ()
 2154 – Commander Tucker ordered tactical alert after Reed discovered that Soval was captured by the Andorians. ()

 Voyager
 Captain Janeway put Voyager on full tactical alert after at least two Vidiian vessels were detected on long range sensors. ()
 Commander Chakotay put Voyager on full tactical alert prior to its entry into the Northwest Passage. ()
 Captain Janeway put Voyager on 24-hour tactical alert when they were under constant attack by Krenim vessels. ()
 Captain Janeway initiated tactical alert when Voyager was approaching a Species 8472 station in an attempt to rescue Commander Chakotay. ()

de:Taktischer Alarm
Alerts