Tachyon detection grid
A tachyon detection grid was a technique developed by Starfleet as a means of detecting cloaked Romulan warships. The grid used active tachyon beams transmitted between different starships or sentry posts to create a tachyon field; any cloaked ship entering this field would be exposed. The technique was developed by  chief engineer Geordi La Forge in early 2368, although it resembled and was probably derived from crude sensor grid techniques used to detect cloaked ships that had been used as far back as 2154 in the buildup to the Earth-Romulan War. ()

The tachyon detection was first seen in practical use during the Starfleet blockade of the Klingon-Romulan border during the Klingon Civil War. Twenty-three starships successfully prevented a convoy of Romulan supply ships from sending further aid to the forces loyal to the House of Duras, tilting the balance in favor of Gowron, the legally-appointed leader of the Klingon High Council. During this operation, Sub-Commander Sela attempted to disrupt the grid by bombarding the  with tachyons, creating a blind spot. Temporarily in command of the Sutherland, Lieutenant Commander Data recognized her tactic and used the residual tachyons to detect the ships trying to pass through. ()

Following this success, the Romulans suspected that the Federation had a tachyon detection grid to supplement its gravitic sensor net along the border of the Romulan Neutral Zone. ()

By 2373, the Klingons had deployed a tachyon detection grid around the perimeter of their military command base on Ty'Gokor. ()

In the Delta Quadrant, the Swarm used a similar technique to monitor the borders of their own territory, consisting of a series of interlaced tachyon beams. The  crew devised a way to elude this grid by modifying their shields to refract the beams around the ship uninterrupted. ()

See also
Long-range tachyon scanner
Tachyon scan

cs:Tachyonová detekční síť
de:Tachyon#Tachyongitter
Sensor technology