Perimeter alert
A perimeter alert was an alert used by Starfleet and the Cardassian military, to warn about an approaching, unidentified starship.

In 2364, Wesley Crusher, while sitting in the command chair on the , flipped open a control panel and told Captain Jean-Luc Picard of a perimeter alert when an alien entity approached Deneb IV. When Picard ignored him, Lieutenant Worf informed him of the same alert. ()

In 2371, a Cardassian perimeter alert in the Almatha sector was believed to be caused by the Maquis-controlled , which later turned out to be false. Outpost 47 then reported another perimeter alert, this time actually caused by the Defiant. () 

In 2372, Tom Paris announced a perimeter alert when the Vidiians approached the . ()

See also
Proximity alarm
Proximity alert

Alerts