The discovery of X-rays at the end of the 19th century led to fantasies of glasses that could see through walls – and clothes. But have those ideas now become reality?

“I have seen my death!” Anna Bertha Röntgen is said to have exclaimed upon seeing the first X-ray photograph ever made – an image of the bones in her hand. It was her husband, German physicist Wilhelm Röntgen, who discovered X-rays in 1895.

The news that someone had found a way of peering through human skin and flesh to look at the skeleton beneath, without so much as touching the subject, was an international sensation. Soon, X-ray photographs revealing bones and even the shadowy impression of internal organs were being published in newspapers around the world.

And it wasn’t long before the fantasy of X-rays entered popular culture. “Around her ribs, those beauteous twenty-four, Her flesh a halo makes, misty in line, Her noseless, eyeless face looks into mine. And I but whisper, ‘Sweetheart, Je t’adore’,” read the lines in one poem published in Life magazine a year after Röntgen’s discovery. X-rays were both sexy and seen as a sort of superpower – an idea eventually made immortal by the 1940s writers of Superman comics. They gave their hero – what else – X-ray vision.

But all the while people hoped that the wonder of X-rays could be theirs to play with. The technology was most commonly imagined as a form of X-ray specs that could see through walls. But has anyone ever made it a reality? Long the subject of science fiction, it might now be close to becoming reality.

In the months and years after Rontgen made his discovery, there was no shortage of brainstorming around what X-rays might allow people to do. To take one example, in 1896 a magazine in Dundee reported on the musings of the local chief constable who was considering how X-rays might be adapted “for detective purposes”. A handheld X-ray device similar to a pair of binoculars could, the magazine suggested, be used to spy into rooms where “shebeeners” – those who sold alcohol without a licence – were plying their trade.

One exhibition promised visitors the ability to ‘see through a sheet of metal’ or ‘count the coins within your purse’

“There’s a lot of X-ray fiction around at that time,” says Keith Williams, a senior lecturer in English at the University of Dundee. “And one article about electric waves actually ends with the scientific journalist speculating about the possibility of being able to see through walls into the most intimate spaces and people’s most private actions.”

There were also some more fanciful public demonstrations of X-rays. One exhibition promised visitors the ability to “see through a sheet of metal” or “count the coins within your purse”.

In reality, though, early experiments with X-rays were confined to medical and scientific applications. Practitioners delighted in producing photographs of complete animal skeletons or tweaking the technique to create sharper X-ray images.

Rontgen himself had been experimenting with a Crookes tube – a scientific instrument which accelerates electrons into a beam known as a cathode ray. A tiny portion of the energy from this process is released as photons. In the electromagnetic spectrum, it’s the wavelength of photonic waves that defines whether they are, for example, radio waves, visible light waves or – as in this case – X-rays. A fluorescent screen revealed that Rontgen’s rays were passing through some materials, like muscle, but not others – such as bone.

Although the harmful effects of frequent exposure to X-rays were soon discovered, the exciting promise of X-ray vision never really went away. X-ray specs, a novelty item often sold via boys’ comic books and magazines, were first patented in 1906. The glasses don’t use X-rays at all, of course. Instead they create a sort of double vision illusion in which the overlapping of objects suggests – not very convincingly – that they have been penetrated to reveal an internal structure.

But in 1998 the promise of X-ray specs took an unexpected technological twist. Sony had been marketing a new range of camcorders with night-vision capabilities – a function the company branded “NightShot”. A few enthusiasts claimed that under special circumstances it was possible to see through people’s clothes to an extent. It was erroneously rumoured at the time that Sony had to recall some of the models in an effort to tackle bad press;in reality the firm just made some modifications to the cameras’ design.

You can see through bushes and stuff but there’s not a whole lot more beyond that – Vince Houghton, International Spy Museum

But night-vision equipment continued to be the subject of hobbyists’ experiments. One YouTuber has uploaded what appears to be a demonstration of how a Sony camera released in 2002 can be quickly modified with some tape and an infrared filter to achieve the desired “X-ray effect”. The video shows how the cover of a book – and even his wife’s bra (which she declined to demonstrate herself) – can be seen through his black t-shirt. “There ya go,” he says, “X-ray vision”.

Night vision works by detecting infrared light, which humans can’t normally see, and converting this energy into visible light waves.

It might just be that the clothing used in this example reveals more when viewed in infrared, suggests Alistair Brown, product manager at British night vision and thermal imaging firm Thermoteknix. This, he adds, could make it look, “very different from broadband visible wavelengths used by our eyes”.

Vince Houghton, an ex-US army soldier and historian at the International Spy Museum in Washington DC, frequently used night vision and thermal imaging technologies in the army. But he says the “X-ray” capabilities are strictly limited.

“You can see through bushes and stuff but there’s not a whole lot more beyond that,” he comments. “If you have a solid structure it’s very difficult to see through with infrared.”

But that doesn’t mean there isn’t a need for this technology. Houghton gives the example of a hostage situation.

“If you can see inside when you decide to finally breach, you know where the bad guys are,” he says.

Has anyone come up with a device that can do this? The answer, surprisingly, is yes. While X-rays remain impractical for anyone but specialists to play with, military contractors have long been experimenting with them. So much so that the idea once posited by Dundee’s 19th Century chief constable has finally come to fruition.

A much cheaper and safer technology offering X-ray specs-like capabilities is one you already have in your home – wi-fi

“The early experiments with this were these huge bulky machines that were not tactically useful if you’re thinking about a military or police operation,” explains Houghton. But now police and military personnel have the option to buy a MINI Z X-ray gun – a handheld, “easy to use” X-ray device that can peer into vehicles, rooms, bags and packages.

“As an operator scans a target, an image appears in real-time on the system’s dedicated tablet,” boasts manufacturer American Science and Engineering on their website. There is also a web page where anyone can try a virtual demo of the system. 

Still, the MINI Z isn’t available to the average consumer and it costs $50,000. What’s more, there have been some concerns that increasing use of X-ray devices by law enforcement might carry health risks to the general public. Similar concerns have been levelled at millimetre-wave scanners – which use microwaves – now installed at many airports. These have faced the added criticism that they are an invasion of privacy, given that operators of some devices are able to see through people’s clothes. To combat such fears, US regulation now prohibits the rendering of detailed images.

However, a much cheaper and safer technology offering x-ray specs-like capabilities is one you already have in your home – wi-fi.

Last year, the Massachusetts Institute of Technology published a video that shows how a custom-built wi-fi transmitter can be used to create a rough image of someone – through a solid wall.

“When you send a wireless signal, it reflects off everything and those reflections come back to you,” explains Dina Katabi. Computer software is able to analyse signal reflections and produce an image of the object from which they have emanated.

It’s possible, of course, that military and intelligence agency personnel are already using advanced versions of this technology for surveillance purposes

“We can image how people move about a space, where they sit, how they walk around and also detect falls – which is a big thing for older people,” adds Katabi.

For Houghton, the technology has a range of potential uses.

“I know for a fact that some of this technology is already being used for building inspection,” he says. “You have the ability to check out wiring and structure.”

It’s possible, of course, that military and intelligence agency personnel are already using advanced versions of this technology for surveillance purposes.

“Anything that you’re seeing in the public news is 10 years behind what the intelligence agencies are probably using,” says Houghton.

He adds that this effectively means we’ve probably come full circle on the century-long dream of X-ray specs. If smart glasses do one day become popular, it’s not hard to imagine future, miniaturised versions of these technologies getting built in to wearable devices.

What was once a foolish notion in the pages of a comic book may soon become a reality. Even Superman would be amazed.


Join 600,000+ Future fans by liking us on Facebook, or follow us on Twitter, Google+, LinkedIn and Instagram.

If you liked this story, sign up for the weekly features newsletter, called “If You Only Read 6 Things This Week”. A handpicked selection of stories from BBC Future, Earth, Culture, Capital, Travel and Autos, delivered to your inbox every Friday.