Security alert
A security alert was a type of alert signal aboard starships and space stations, primarily for internal security purposes. It was similar to an intruder alert, and could be initiated explicitly by personnel or triggered by predefined parameters.

In the 23rd century, a security alert aboard Federation starships was part of the general quarters alert, and had at least three levels. ()  By 2285, security alerts of Federation starship systems such as the  were separated from the general quarters alert. ()

In the 24th century aboard  and  starships, security alerts had at least five levels of application (also referred to as conditions), each one for different types of situations. On certain space stations, security alerts were distinguished by color. A security alert could be activated with no stated degree. The ship's security chief was responsible for initiating shipboard security alerts. ()

Levels/Conditions

Level/Condition 10 
Aboard the , Captain Kathryn Janeway instituted a level 10 security alert after more former Maquis members now part of her crew were subdued by an unknown assailant. The action also confined non-essential personnel to quarters, and the posting of security teams on all decks. ()

Level/Condition 4 

Aboard the Federation starship , Captain Jean-Luc Picard ordered a level 4 security alert in 2369 after it became apparent that crewmembers were mysteriously disappearing from the vessel. ()

Around stardate 46731, the Enterprise-D was on level 4 security. ()

Level/Condition 3 
Picard asked Worf to maintain a level 3 security alert after Lieutenant Reginald Barclay reported seeing alien lifeforms while in an extended transporter beam. ()

Picard once again instituted a condition 3 security alert and told the computer to shut down all transporter systems and shuttlebays as Wesley Crusher eluded the crew while they were under the influence of the Ktarian game. ()

Tuvok called a level three security alert aboard Voyager and told all hands to report to duty stations in an attempt to apprehend the mutating Tom Paris. ()

Level/Condition 2 
In 2369, Picard ordered a level 2 security alert, after it was learned that a faction of the Borg had changed their entire existence and a new objective. They were no longer interested in acquiring cultures and technology. Armed guards were posted on every deck. ()

In an alternate timeline created by Q, Picard ordered a level 2 security alert in 2364 after he continued to experience shifting through time. ()

Level/Condition 1 
Geordi La Forge, seemingly filling in for Worf as security chief, suggested the Enterprise should go to level one security alert while trying to apprehend the devolving Klingon. ()

Colors

Yellow
Benjamin Sisko told Kira Nerys to go to security alert yellow when the Norkova started docking. ()

Black
Code Black security alert was an alert status utilized by Cold Station 12. This alert locked down access to Augment embryos and several dangerous diseases that were stored on the station. ()

Full alert
Commander William T. Riker called for a full security alert when criminals inhabiting three of the Enterprise crew's bodies attempted to gain control of the ship. ()

Sisko put the entire station at full security alert, and also ordered for all turbolifts secured and to seal off some airlocks. ()

Captain Janeway told Chakotay to put Voyager into full security alert in response to the newly realized threat from the Vaadwaur. ()

General alerts
Picard called for a security alert to all decks when Ira Graves, who took over the body of Data, attempted to take over the Enterprise. ()

Worf told the bridge to institute a security alert when he found  dead in engineering. ()

Chief Miles O'Brien was interrupted while attempting to call a security alert by an alien intruder in Transporter Room Three. Worf expanded the alert to all decks after the intruder left the transporter room. ()

Picard told Worf to be on security alert when he realized the potential danger of Clara Sutter's imaginary friend. ()

Data called for a security alert as a mercenary ship fled from the Enterprise. ()

Riker called a security alert to all decks when alien intruders were expected to transport aboard the Enterprise. ()

Altovar triggered a security alert when he broke into the infirmary of Deep Space 9. ()

While Tieran had control over Kes' body, Janeway called a security alert as Tieran tried to escape from Voyager. ()

When Chakotay realized that the translocation by the Nyrians to the  was most likely a ploy to take control of the ship, he issued a security alert to all hands, though there were only twelve other crewmen on board at the time. ()

Ensign "Gentry" tried to call a security alert to "Headquarters". ()

When Seven of Nine resisted an attempt to place her in stasis as the crew of Voyager prepared to enter a bioplasmic organism they believed to be a wormhole leading them to Earth, Chakotay declared a security alert. ()

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Alerts