Dave Bailey listens to navigation beam

Dave Bailey utilizes an earpiece to monitor the Enterprise's navigation beam

A navigation beam was a directed-energy transmission utilized by starships for the purpose of identifying information regarding ship's position, speed, etc. This information would then be relayed back to the ship's navigator, sometimes via earpiece.

In 2266, when the USS Enterprise encountered the extremely powerful First Federation flagship Fesarius, all efforts by the Enterprise crew to establish communications met with failure, until Balok, the Fesarius's master, began transmitting a message over the Enterprise's navigation beam, a message which was subsequently detected by Dave Bailey, the ship's navigator. (TOS: "The Corbomite Maneuver")