An isodyne relay is a component of a 24th century Starfleet tricorder.

On AR-558 in 2375, Ezri Dax suggested cross linking the isodyne and optronic relays of a tricorder to detect the Jem'Hadar's "Houdini" mines while they were in subspace. Kellin was impressed by her suggestion. (DS9: "The Siege of AR-558")

While investigating Species 8472's simulation of Starfleet Headquarters in 2375, Commander Chakotay claimed to Boothby that the isodyne relays in his tricorder were malfunctioning, causing it to register bamboo as maple trees. (VOY: "In the Flesh")