Tennis Equipment

Cyclops in Tennis: Assisted Line Judging Before Hawkeye

A service line monitor that used infrared beams to determine whether a serve was in or out. But how did it work?

A recent comment asked about the loud beeping noise heard throughout the 1980s, 1990s and early 2000s when a serve was long and what it was.

The answer, of course, was Cyclops, the very first electronic line judging aid which was first used at Wimbledon in 1980.

Let’s take a look at the technology that paved the way for future aids such as the electronic net machine and later Hawkeye. And keep reading to learn a fun fact about Roger Federer and Cyclops!

What Was Cyclops?

how to choose

Cyclops was the first line monitor used to assist officials in tennis. It was developed by inventor Bill Carlton and Margaret Parnis England in 1979. The system was quickly adopted by Wimbledon in 1980 and went on to be used at the US Open and Australian Open. Like Hawkeye, it was never used on clay as the undulating surface and dust particles caused problems

It was only ever used to determine if a serve was in or out and was activated by the umpire before each service point. Then deactivated when the service was good. 

While no statistics were ever provided to prove it’s efficacy, it was never a hugely controversial system. In the main, it was used as a complement to the line judges, not a replacement and the line umpire had the final call. In some matches, the system was shut down if there were questions about its accuracy or the dreaded ‘phantom beep’. 

Cyclops in Action – The ‘Whistle’ Sound

The sound changed to a beep as the crowd had begun imitating the whistle and it wasn’t easy for those sat away from the court to hear it.

How Cyclops Worked

Cyclops Tennis

The Cyclops system was installed at the side of the court by the service box. The setup was two boxes both of which were in line with the service box line.

One of the Cyclops boxes emitted five infrared beams across the court (around 10mm off the ground) to the other box known as the receiving box. This was also connected to a smaller control box held by the service line umpire. And of course, there was an identical setup on the other side of the net.

One infrared beam ran along the good side of the service box line, and the other four ran outside the service line, up to 45 cm from the line.

When a ball hit was good (or just inside the line) it broke the first beam and turned off the others. If the serve was long, it broke one of the four other beams.

In the first scenario, the control box signalled with a green light that the first line had been broken and the serve was good. If the ball broke any of the others without breaking the first beam, it signalled with a red light and a loud beep.

The beep that most of you guys will remember was actually a whistle when the system first burst onto the scene but after the crowd starting mimicking it, it was switched to a beeping sound as this was also deemed clearer to hear in a loud stadium.

The system only worked for close calls and serves that weren’t close to the infrared beams were considered easy pickings for umpires and line judges to determine purely by eye.

Why Was Cyclops Only Used for Serves?

Fed Serve

Cyclops was limited to just serves because it had no idea what object was breaking the beam. In fact, there were times when foreign objects caused phantom beeps such as insects and dirt in the wind, although it was improved over time to be less sensitive to light and other objects.

However, on the baseline and sidelines, players are continually crossing the lines with their feet and racquets. The system would be going off every time a beam was tripped.

As a result, Cyclops had to be switched off (the umpire pushed a button on the control box) immediately after a good service so another ball, racket or the player’s feet by the service line do not trip the beams again, triggering a beep.

Fun Fact: Roger Federer could not have used the SABR with Cyclops. Had he got close enough to the service line before the ball had bounced then he’d risk breaking one of the beams and triggering the beep!

Sneak Attacks by Roger – Impossible Under Cyclops

What Happened to Cyclops?


The introduction of Cyclops marked the advent of electronic aids to assist officials in tennis and that naturally meant other systems were always going to hit the market that were more effective.

Cyclops twenty-five year run came to and end in 2005 with the launch of Hawkeye. The US Open was the first to replace it in 2005, followed by the Australian Open and then Wimbledon replaced it to use hawkeye for the first time in 2007.

Once the slams got rid of it, it was quickly replaced en masse and condemned to the rubbish bin of history with the superior, more accurate and all-encompassing hawkeye taking the reigns.

To my knowledge, it’s no longer in use at any tennis tournaments but it certainly paved the way for future technology.

Did you guys know about Cyclops? Or did you only start watching when it had already been replaced? Let me know in the comments.

PS. I was hoping to find a clip on YouTube of the iconic beeping sound but wasn’t able to. If you know of one, please comment below.


Editor of Perfect Tennis and a big fan of Roger Federer, I've spent countless hours watching and analysing his matches. Alongside playing the sport, I also enjoy writing about the tour, rackets, strings, and the technicalities of the game. Whether it's breaking down the latest tournament results or discussing the latest gear innovations, I'm always eager to share my insights with fellow tennis enthusiasts.

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    1. I managed to miss out on this article somehow.

      No, you’re not thinking of the sensor that replaced the net cord judge, are you?

    2. Hi, the product was invented by Bill Carlton , however it was his concept that was designed and manufactured her in the U.K. by Radiovisor Ltd. At the time my father was a director (Managing) of the company and Bill came across to crash out design many a time . In later years he would attend with his daughter Sarah who I believe eventually took over the business.
      Unfortunately Cyclops became redundant as new technology took over around the same time as Sarah took the lead from Bill.
      Simultaneously Radiovisor went through changes. Although I held company Radiovisor ltd and some of its employees for many years ahead , we no longer manufactured Cyclops.
      A word should be said for Terrance Murphy who was the chartered electrical design engineer who was employed by Radiovisor and responsible for Cyclops design. Terrance otherwise know as Mick Murphy was an X Marconi Radar technician and worked for the Radiovisor in one form or the other for over 25 years and wad working part time during semi retirement when he tragically lost his life .

    1. Haha cheers. It was a good idea for a blog post. I wouldn’t have thought of it until you asked. I imagine a good chunk of people who frequent the blog don’t know about pre-hawkeye tennis tech 🙂

      1. Hmm I would be interested to know the demographics of most tennis viewers. I am guessing it’s 40+ tbh. I am not sure the game does a good job of appealing to younger audiences?

        What is the average age of a tennistv subscriber for example?

    2. I guess, Jonathan writes articles every day (and night) and packs them to drawers. He must have so far ready articles about everything, so it’s not a big work to find the right one for today 😉 Assuming the drawers have some quick search engine (maybe Jon’s patent?) 🙂

  1. I started to watch tennis in 1988 and I remember the beep, but was not really aware it was used for serve :-). Thanks Jon for the great post.


  2. I started watching tennis in the seventies and the only sound signals available at the time were a deluge of shouted slang and intimidating questioning by John MacEnroe. He usually took turns with a certain Mr. Connors.
    I guess we could call it a dual timbre signaling.

    1. Both those two were an embarrassment to sport. I just watched a clip of Connors running to the other side of the court to rub out a mark before the ump could see. And you can find JMac on youtube in all his glory. What I don’t like about him commentating is his ramblings about his past career and how proud he seems to be about the bad behaviour. Otherwise, knows his stuff but the commentators start praising the one winning the match…ever notice that? Ok, rant over.
      I believe it was at the USO this year when a ball was way out (shown on replay) and hawkeye chose the wrong ball. Not a foolproof system.
      Thanks for the write-up, Jonathan! The fast and the furious! Lots of lattes?

      1. I haven’t seen that hawkeye thing. Is there a clip? I am guessing that is user error selecting the wrong ball on the computer rather than it messing up where it landed?

      2. I believe Hawkeye is supposed to chose the last ball automatically. Yes, the error was in choosing the ball, not where it landed. I think it was a Dimi match? Against Medvedev? Ball was way out.

  3. Great article again on a long forgotten aid in tennis. However, I always thought it had to do with the net.
    Thanks Jonathan

  4. Interesting article. Thanks! Why don’t you write a piece on the hawkeye system too? I find it fascinating, but haven’t really figured out how it works. Maybe you already have it in the drawer? 😉

      1. I have little doubt that sooner or later the hawkeye (or other) will he able to warn in real time when a ball goes out without the need to create a break in the gameplay.

        Anyway, what about the “real bounce”? That one is using real filming in high speed. It seems to be quite accurate.

  5. Hey Jonathan, one question (and I hope I can formulate it properly):
    You know the margin error of Hawk Eye, ¿right? Certain millimeters.
    ¿How is that? ¿It is included in the mark of the bounce, so it becomes a little bigger, or it means just about the placement of the mark and that could differ from the reality (a couple of mm to one side and upwards, etc)?

    1. By “included”, I meant that the area of the mark covers more space than it should, to include that margin of error. I hope to be clear about it.

    2. I don’t think it has anything to do with the bounce. I think it’s just their margin for error due to all the variables with the conditions, cameras etc…

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