Cyclops was an electronic tennis system to judge whether serves were in or out.
It used infrared beams along the service line to detect the ball's landing spot. Cyclops made a beeping sound when it detected a fault serve. It was used at major tournaments like Wimbledon from 1980 to 2007.
The system helped reduce arguments about close-line calls on serves. Players like John McEnroe and Ilie Nastase famously interacted with Cyclops during matches.
Cyclops was eventually replaced by the more advanced Hawk-Eye technology. It was an important step in bringing technology to tennis officiating.