A tracer was Ramuran security operative whose purpose was to track down and retrieve those who attempted to leave their world. One tracer, called Kellin, was a trained expert in weaponry, surveillance, fighting skills, and held a high security clearance. Tracers were said to never go home empty-handed, as the disgrace would be too great. To the knowledge of Kellin, no one had ever managed to permanently escape the tracers.
Tracers might hide themselves and their ships with polarization cloaks, and they used computer viruses to eliminate any records of their presence. They were armed with neurolytic emitters, with which they erased the memories of their targets, making them more cooperative.
Kellin was a tracer who tracked the fugitive Reskat for over a year, ultimately finding him hiding on USS Voyager in 2374. She was found by the Voyager crew and spent several weeks tracking him down with their help. After she fulfilled her mission, she found that she had developed feelings for Commander Chakotay and returned to Voyager as a fugitive herself. She was hunted by more tracers, one of whom, Curneth, infiltrated Voyager and erased her memories. As a result, Kellin returned willingly with him to Ramura. (VOY: "Unforgettable")