John Carmack has been building a virtual reality headset in his spare time. He's showing it to people behind closed doors at this year's E3, tucked away inside the Bethesda booth, and described it as "probably the best VR demo the world has ever seen." Our video hero, David Boddington, was the 30th person in the world to use it.

Check below for a 20 minute video with Carmack on virtual reality, why he decided to tackle headsets, the latency of the human mind, and the first footage of one his handmade prototypes.

Carmack's such an intelligent guy that a single question sends him off on a four-minute-long monologue with a dozen long words I don't understand. To help make it easier, we've split the 20 minute video in to three chunks, with some impressions at the end of what it's like to use.

Part one shows the first glimpse of the duct-tape-and-belt prototype, covers the latency of the human brain, and how making "an 8 year old PC game is still demanding on consoles". Also big words about screens I don't understand?

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Part two is the most impenetrably techy, as he explains the exact challenges of building a VR headset, but Carmack occasionally surfaces from the jargon to say something incredibly concise and exciting. Like when he explains that this is the best VR demo that the world has ever seen, but that "maybe hidden in some NASA lab there's something cooler than this, but I haven't seen it."

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The third part is where Carmack gets down to showing us the device itself, while Games Radar 's Hollander Cooper quizzes him on the realities of bringing something like this to market. Key quote? "This is literally held together with duct tape, but the guts of this is going to be made available as a kit for around $500."

At that price, I'd buy one.

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Carmack talked a bit more in this last part on the reasons why the project excites him. "For a certain part of the hacker/maker crowd, this is going to be awesomely cool to work with, because there is honest to god cutting edge research to be done on the ergonomics, the focusing adjustment, software integration with other titles. These are things that people can do in their workshop that can make a difference in the next twelve months and yes, somebody big is going to turn this in to a real product in the coming years."

Our video wizard David Boddington used it to play Doom 3: BFG Edition and loved it. "The level of immersion was unlike any other gaming experience I've ever had, and that bodes well for the future if Carmack or someone else can take the tech to the next level."

It's worth noting that the prototype Carmack is demoing wasn't made by him, but by another Texan builder of VR headsets. It's using the same tech and principles as Carmack's own version, which was unfortunately unable to make the trip to E3.

The goggle screens completely cover your vision, meaning the only thing you can see are scary corridors and flying heads. Character movement works more traditionally however, with players using a controller to walk around and shoot, while the goggles function as a head-tracker. If it ever comes to market as a consumer product, or even if the maker kits are reasonably accessible, it sounds like the perfect thing for hardcore ArmA players or flight sim enthusiasts.

There's one final thing that's interesting about this. Carmack has been good friends with Michael Abrash since the pair were programmers together on Quake 1. What did Michael Abrash recently say he was working on at Valve? Wearable computing.

Would you wear virtual reality goggles in front of your PC? Do you think John Carmack can make VR finally good?