A directional locator was a communications technology used aboard Template:ShipClass 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 Starship Enterprise 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 onboard the Enterprise. (TOS: "Journey to Babel")