Internal sensor.

The internal sensors displayed
on a monitor

Internal sensors were sensors aboard starships and starbases that were used to scan for various things, including life signs, inside the vessel or structure. They performed such functions as locating various crewmembers via combadges and detecting intruders. Internal sensors were used to locate an intruder during an intruder alert situation.

In August of 2151, T'Pol asked Shaw aboard the Earth Cargo Service freighter ECS Fortunate why the power of the internal sensors was rerouted to the weapons system. Shaw replied that the Fortunate was in a battle with the Nausicaans. When T'Pol told him she would remove this bypass as the freighter was no longer in a battle situation, Shaw told her to leave that the way it was. (ENT: "Fortunate Son")

In 2151, the unidentified aliens placed a device on board Enterprise which was tapped into most of the ship's systems, including internal sensors and communications on all decks. (ENT: "Silent Enemy")

In September 2152, Commander Trip Tucker accessed the internal sensors aboard Enterprise from a monitor in T'Pol's quarters to have a closer look at the intruders from the Takret Militia on the bridge. (ENT: "The Catwalk")

In 2154, Lieutenant Reed used the internal sensors of Enterprise NX-01 to locate the Vulcan bio-signs of Soval but was unable to find him on board. (ENT: "Kir'Shara")

In 2155 in the mirror universe, T'Pol disabled the internal sensors on the ISS Enterprise to aid in her attempt to free Captain Maximilian Forrest following Jonathan Archer's mutiny. (ENT: "In a Mirror, Darkly")

The internal sensors of a Galaxy-class starship were unable to detect 15,525 known physical substances, including 532 substances which could exist in an oxygen atmosphere. (TNG: "Hollow Pursuits")

When the USS Defiant traveled back in time due to the actions of Arne Darvin, who wanted to kill James T. Kirk, Captain, Chief Miles O'Brien warned Doctor Julian Bashir to keep his scans for Darvin within a scan field below twenty milliwatts or else it would trip the internal sensors of the USS Enterprise. Later, Sisko and the others used the internal sensors of the Enterprise to scan for explosives. (DS9: "Trials and Tribble-ations")

The internal sensors were used to locate Wesley Crusher when he was the only crewmember, besides Data, unharmed by the game Riker brought back from Risa. The sensors were able to locate him, despite him not having his combadge on, by registering him as an unidentified heat source. (TNG: "The Game")

When strange sensor malfunctions began to appear on the USS Enterprise-D in 2368, Commander Riker ordered a level 3 diagnostic of the entire internal sensor network. (TNG: "Schisms")

Chief Miles O'Brien called the internal sensors aboard Deep Space 9 "bloody Cardassian internal sensors" because they were not sensitive enough. A recalibration of these sensors would take days. (DS9: "Q-Less")

In 2370, while talking to Worf in Ten Forward, Ensign Sito Jaxa mentioned that among her duties at ops was to find a lost puppy and that she used the internal sensors for this task. (TNG: "Lower Decks")

That same year, when Doctor Julian Bashir was trapped in a version of Deep Space 9 created by his own mind, he wanted to find a computer processing junction so that O'Brien could repair the station's internal sensors. According to O'Brien, the entire sensor array was burned out. (DS9: "Distant Voices")

In 2372, a mutated Tom Paris caused a power outage on board the USS Voyager after firing a phaser at a port plasma conduit. Commander Chakotay reported to Captain Kathryn Janeway that he couldn't get power to the internal sensors. (VOY: "Threshold")

When the Borg took over control of deck 16 aboard the USS Enterprise-E, the crew lost the internal sensors as well as the environmental controls. (Star Trek: First Contact)

In 2373, when Captain Kathryn Janeway and Neelix found Voyager adrift after returning from a three-day trade mission with the Tak Tak, Janeway tried to access the ship's internal sensors, but found that the main computer was offline. (VOY: "Macrocosm")

The internal sensors of Deep Space 9 were able to monitor levels of chroniton buildup during an explosive confrontation between a Prophet (in the body of Kira Nerys) and a Pah-wraith (in the body of Jake Sisko) in 2374. (DS9: "The Reckoning")

In Lieutenant Tuvok's Insurrection Alpha holoprogram, the internal sensors were part of a code involving a Maquis mutiny on the USS Voyager. As part of the program, Commander Chakotay would ask the participant in the program if they had finished upgrading the internal sensors. If the participant replied in the affirmative, it was supposed to actually indicate that they had placed all crew quarters on lock-down. (VOY: "Worst Case Scenario")

In 2376, when Seven of Nine presented her theory regarding a conspiracy on-board the USS Voyager to Commander Chakotay and later Captain Kathryn Janeway, she first sealed the doors and then disabled the internal sensors within astrometrics. (VOY: "The Voyager Conspiracy")