Intruder alert

AT: "xx" Intruder alert was an alert status on Federation starships and space stations. It could be declared at any time, by any member of the crew upon sighting an intruder on board. It could also be activated automatically based on predefined criteria, such as entering a restricted area. The alert was announced by audio and crewmembers were expected to take appropriate action.

In 2364, Wesley Crusher rushed to the bridge to warn of an impending intruder alert he detected while experimenting with ship's long range sensors. The warning is immediately confirmed by Tasha Yar and an audible alert over the ship's Comm. This type of alert is later referred to as a Proximity alert or Proximity alarm to differentiate an approaching vessel from a shipboard intruder. (TNG: "The Battle")

In 2367, Captain Jean-Luc Picard attempted to sound an intruder alert when "Ardra" appeared in his quarters. (TNG: "Devil's Due")

In 2369, Miles O'Brien activated the intruder alert and called a security team into his quarters when the fictional character Rumpelstiltskin appeared in Molly's bedroom. (DS9: "If Wishes Were Horses")

In 2371, when the energy patterns of the Komar and Chakotay were forcing the crew of the USS Voyager to perform actions against their will, Kathryn Janeway initiated an intruder alert. (VOY: "Cathexis")

In 2372 of an alternate timeline, the computer of the USS Yellowstone declared an intruder alert and that there was an unauthorized launch in progress when Ensign Harry Kim and Tom Paris hijacked it. (VOY: "Non Sequitur")

Rom activated an intruder alert which was detected by Damar after Odo failed to deactivate the alarms on a conduit leading to an EPS feed. (DS9: "Favor the Bold")

In 2373, Captain Kathryn Janeway underwent a mind meld with Lieutenant Tuvok to try to determine the source of an apparent repressed memory. In the meld, she was sent to the bridge of the USS Excelsior in 2293 in Tuvok's memory. A disruption of the meld caused the Captain Hikaru Sulu of the memory to notice her presence and he declared an intruder alert, but she and Tuvok solved the problem by returning to an earlier stage of the memory, in which she was able to steal an appropriate Starfleet uniform to blend in. (VOY: "Flashback")

That same year, when the holographic character Marayna appeared in Tuvok's quarters despite having apparently been deleted, Tuvok called for an intruder alert, but she used her control of the Voyager computer system to silence it. (VOY: "Alter Ego")

Also that same year, when The Doctor realized that macroviruses had infested Voyager's mess hall, he declared an intruder alert on deck 2, Section 13. (VOY: "Macrocosm")

In Lieutenant Tuvok's Insurrection Alpha holoprogram, the Voyager computer declared an intruder alert on deck 8 when the Lieutenant Tom Paris and Captain Kathryn Janeway of the program transported there. (VOY: "Worst Case Scenario")

In an alternate timeline, Neelix helped repair the internal sensors aboard the USS Voyager after they had been seriously damaged due to repeated Krenim attack. He wanted to try several variations on the audio warning, but security chief Tuvok ordered him to keep the standard alert. (VOY: "Year of Hell")

Tuvok initiated an intruder alert and called for security to deck one when the two astronauts from the planet that Voyager was trapped above in orbit transitioned into Voyager's timeframe. (VOY: "Blink of an Eye")

In 2374, the crew of Voyager initiated an intruder alert when they discovered that a member of Species 8472 had penetrated their hull and invaded the ship. (VOY: "Prey")

In 2376, Lieutenant B'Elanna Torres jokingly declared "intruder alert" when her old boyfriend Lieutenant Maxwell Burke accessed a command station in engineering without her prior authorization. (VOY: "Equinox")

In 2377, Lieutenant B'Elanna Torres declared an intruder alert when she and Seven of Nine found Fantome hiding in one of Voyager''s cargo bays. (VOY: "The Void")

In 2378, the Voyager computer reported an intruder alert when the Talaxian child Brax snuck aboard the vessel. (VOY: "Homestead")

Intruder alert was also known as "general quarters security condition three". (TOS: "The Man Trap")