An electronic line judge is a device used in tennis to automatically detect where a ball has landed on the court. Attempts to revolutionize tennis officiating and the judging of calls in the sport began in the early 1970s and has resulted in the design, development and prototyping of several computerized, electronic line-judge devices.

Hawk-eye is a technology used in tennis for determining if the ball is in or out. This line-calling system uses multiple camera angles to trace the tennis ball's trajectory. Hawk-Eye uses six or more computer-linked television cameras situated around the court.

Since 2017, WTT has used Hawk-Eye Live, an automated line-calling system created by the same company that handles tennis’ electronic challenge replays. Instead of relying on line judges to make calls, Hawk-Eye’s cameras and computers do the job themselves, complete with human-sounding “out” calls.

This electronic line calling system uses contact sensors physically embedded in the tennis lines. The sensor looks like a co-axial cable (a long ribbon with integrated insulated wires embedded in it). The ribbon is only.2 millimeters thick and can be completely covered with the coating material used to cover hard courts.