A Borg polaron beam
A polaron beam (alternatively called a polaron scan) was a type of ship-based sensor which used polaron particles to scan other vessels.
Jem'Hadar fighters had the capability to conduct polaron scans and also used phased polaron beams as weapons. In 2373, the IKS Rotarran detected one such vessel conducting polaron scans of the surrounding space, though it was unable to detect the cloaked Klingon bird-of-prey. (DS9: "The Jem'Hadar", "Soldiers of the Empire")
Borg cubes possessed polaron beams, capable of scanning through Federation shield technology. In 2373, one such cube momentarily stopped to scan the USS Voyager during the pursuit of a Species 8472 bioship. (VOY: "Scorpion")