(covers information from several alternate timelines)
Neutrinos are elementary particles which belong to the lepton family of particles. They have very small masses, and hence travel at close to the speed of light. Although they interact very rarely, a starship's sensor array contains instruments capable of detecting them.
The presence of elevated neutrinos may indicate the presence of a ship – possibly cloaked. The Bajoran wormhole also emitted neutrinos before opening, giving Deep Space 9 a moment to prepare before any ship came through.
- Antimatter reactors were known to produce neutrino emissions. In 2151, after detecting neutrino emissions from the Akaali homeworld, Sub-Commander T'Pol realized that an antimatter reactor might be present on the planet. (ENT: "Civilization")
- A tunneling neutrino beam can be used to remove subatomic bacteria from a starship. (TNG: "A Matter Of Honor")
- Doctor Paul Stubbs used neutrino velocity spectrometry imaging from his egg probe to scan a binary star system in the Kavis Alpha sector. (TNG: "Evolution")
- Wesley Crusher suggested using a neutrino pulse to cut through interference on Galorndon Core and signal Geordi La Forge when he was trapped there. La Forge saw the pulse with his VISOR and made his way to the beam-out site. (TNG: "The Enemy").
- Duras accused Mogh, Worf's father, of sending coded neutrino pulses to signal the Romulans, leading to the Khitomer Massacre. (TNG: "Sins of the Father").
- Wesley Crusher suggested adding pre-processors to the USS Enterprise-D's neutrino counters to boost efficiency. (TNG: "Ménage à Troi").
- When the Enterprise-D had apparently passed through a wormhole, Data set out to check the neutrino and heavy particle detectors. (TNG: "Clues")
- Timicin, a scientist from Kaelon II, considered neutrino counts among countless variables when he experimented with a way to revive a dying star. (TNG: "Half a Life")
- When Wesley Crusher returned from Starfleet Academy to visit the Enterprise and met Robin Lefler, he was so distracted that she had to remind him that his "neutrinos are drifting" as he tried to recalibrate the ship's scanners. (TNG: "The Game")
- Geordi La Forge used a neutrino field to isolate the Enterprise's cargo bay when aliens possessed Miles O'Brien, Deanna Troi, and Data. He hoped it would buy Captain Picard enough time to deal with the aliens. (TNG: "Power Play")
- When a shuttlecraft belonging to the J'naii had disappeared into an area of "null space," Data was surprised to detect a neutrino emission (such as a shuttlecraft might emit) apparently coming from nowhere. William Riker later confirmed that the emission was coming from within the null space. (TNG: "The Outcast")
- Geordi La Forge attempted to infuse a reactor on Tagra IV with neutrinos when it started to overload. (TNG: "True Q")
- Lieutenant Junior Grade Jean-Luc Picard, aboard the USS Enterprise-D in an alternate timeline, suggested neutrino emissions could be to blame for a problem Geordi La Forge was having trouble identifying. (TNG: "Tapestry")
- Severe neutrino disturbances were one factor that lead Jadzia Dax to consider the Denorios belt as a possible location for the Celestial Temple of the Bajoran Prophets. The crew of Deep Space 9 later recognized that neutrino emissions were an indicator that the Bajoran wormhole was opening. (DS9: "Emissary")
- In 2369 Major Kira Nerys informed Commander Benjamin Sisko that they had picked up elevated neutrino readings and that something came through the wormhole. (DS9: "Captive Pursuit", "Dramatis Personae")
- Miles O'Brien observed residual neutrinos in the structure of a building damaged by what he had thought was only an illusion – the Dal'Rok in a village on Bajor. (DS9: "The Storyteller")
- In 2370, Martus Mazur's probability-altering gambling machines caused more than eighty percent of solar neutrinos in Deep Space 9 to spin clockwise. Jadzia Dax noticed that most of the neutrinos on Deep Space 9 were spinning in the same direction, when really the direction of a neutrino's spin should have been random. (DS9: "Rivals")
- Tamal became concerned about a neutrino leak in the port nacelle when Thomas Riker and the Maquis stole the USS Defiant. (DS9: "Defiant")
- Jadzia Dax noticed that certain interference in a ship's transponder signal just before it exploded could have been caused by a forced neutrino inversion, such as the Romulans used in their explosives. (DS9: "Improbable Cause")
- Major Kira Nerys identified a Maquis ship by its neutrino signature in the Badlands. (DS9: "For the Uniform")
- When a Dominion fleet disappeared inside the Bajoran wormhole, Jadzia Dax noticed that there weren't even any neutrino emissions left from the ships. (DS9: "Sacrifice of Angels")
- Evidence of elevated neutrino readings was used to detect the true location of the Cardassian-built Dreadnought weapon, lost in the Delta Quadrant after being appropriated by B'Elanna Torres and the Maquis. (VOY: "Dreadnought")
- Seven of Nine found suspiciously erratic neutrino levels while examining the deceptive living cloud, which was posing as a wormhole leading back to the Alpha Quadrant. This was dismissed by the mind-controlled Janeway. (VOY: "Bliss")
- Icheb designed a high-resolution gravimetric sensor array that scanned for the neutrino flux associated with wormholes to help Voyager get home faster for his science fair project. He got the idea from studying Starfleet records on the Bajoran wormhole. (VOY: "Child's Play")
- The temporal anomaly that shattered Voyager into 37 different timeframes emitted high levels of neutrinos and chronitons. (VOY: "Shattered")
- Data detected neutrino emissions coming from a lake on Ba'ku and, after walking into the lake to investigate, discovered a cloaked Federation holoship. (Star Trek: Insurrection)