Clad in a stylish, black zip-up top and coolly holding the gaze, he could be an upmarket hitman researching his next job. One columnist likened him to “an assassin.”

But that was just mischief, since the New York Times knew the bearded, beanie-wearing man on the New York subway was Google’s Sergey Brin, who, given the company’s storage of billions of internet searches, could already know everything about his fellow passengers.

Look more closely though, and you will see Brin may be learning even more. His glasses are no ordinary over-sized ski goggles but a prototype of the latest gadget that could allow mobile data-downloading with voice commands: Google Glasses.

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Not to be confused with Google Goggles, an app for its Android operating system, Google Glasses have been developed in secret by technologists at the Californian search giant.

Capable of giving an “augmented reality” to viewers – or telling them lots of stuff about who and what they are seeing, they could transform our computer habits beyond even the astonishing advances of recent years.

Thy first received an outing last year when 39-year-old Brin, who is in charge of developing Google X projects – wore them at an event for the blind in San Francisco, in April.

A few more glimpses of them were seen last summer, setting tongues wagging in tech circles, where there was intense excitement about their potential for increasing interaction with the web on the go.

But they looked clunkier than the pair spotted on the subway in the picture taken, by passenger Noah Zerkin who posted it on Twitter today.

Zerkin describes himself as a “wearable computing and augmented reality enthusiast/hardware prototyper,” but told Twitter that he had got into the same subway carriage as Brin by coincidence. He said he had had had “a brief conversation with the most powerful man in the world. On the downtown 3 train. Nice guy.”

According to technologists, Google Glasses could allow humans to interact with their surroundings in a much more dynamic and instantaneous way.

A small screen sits on the right-size of the right lens, along with a camera, microphone and speakers, meaning, potentially, that the user could point the camera at, say, subway passengers and use facial recognition software to inform them of their name, occupation and everything else, such as the time they wore an embarrassing outfit on a train.

Like the company’s Android software, the technology is expected to be made available to developers – possibly later this year. Whether they will be any use on the London Underground is in question though – most stations and trains still cannot receive a signal, no matter how fancy the device.

Brin, a Moscow-born computer scientist, co-founded Google with Larry Page in 1998. He is now estimated to have a personal fortune of more than $20bn.