A bio-scanner was technology used to detect and scan biological entities. Bio-scanners were found in devices such as tricorders as well as starships themselves. The summary of the findings made by bioscanners were reported in a bioscanners report.
Earth Starfleet ships were equipped with bio-scanners since at least the mid-22nd century, though the technology was not perfect. In 2152, the bio-scanners aboard Enterprise NX-01 failed to detect a lymphatic virus brought on board along with canisters of deuterium. (ENT: "The Seventh")
24th century Starfleet tricorders were equipped with bio-scanners. In 2371, Neelix's tricorder picked up a single class 3 humanoid organism on a rogue planetoid that was thought to be uninhabited. (VOY: "Phage") Later that same year, the USS Voyager used its own bio-scanners to investigate new space-dwelling lifeforms discovered in the Delta Quadrant. (VOY: "Elogium")