Perimeter grid
A perimeter grid was a type of sensor net used to detect starships that violated an area of space.

The highly territorial Swarm species protected their space with a form of perimeter grid that utilized a series of interlaced tachyon beams to detect encroaching ships. In 2373, the crew of the  devised a method of entering the grid without being detected by modifying their shields to refract the beams around the ship. However Voyager later encountered a Swarm ship that emitted a polaron pulse disrupting the new shield configuration, making the ship visible to the grid and therefore other Swarm vessels. ()

Until at least 2374, the xenophobic B'omar maintainted a perimeter grid to detect unauthorised vessels entering their space. The grid was sensitive enough to even detect and track small objects in space such as stellar particles. ()

See also
Defensive sphere
Sensor technology