Directional locator
A directional locator was a communications technology used aboard  vessels for the purpose of identifying both the source and reception point of a transmission.

In 2267, while transporting a group of diplomats to Babel, the  detected a covert transmission. Using the directional locator, Lieutenant Uhura was able to determine that the signal was coming from a mysterious vessel shadowing them, and being received by a spy on board the Enterprise. ()
Communications technology