You could spy on someone using a microwave oven as a mic

While too much of our information streams have become infected with endless discussion of the current White House, this week there’s a direct connection to Leon Theremin. So – let’s dive in, shall we?

In case you’ve managed to avoid US news, you might not know that the Counselor to the President of the United States recently speculated to an interviewer that a microwave oven could be used as a spying device, and specifically, as a camera.

And that led to stories like this one:
No, Microwave Ovens Cannot Spy on You—for Lots of Reasons [Wired]

The problem is, what that headline claims is patently wrong. (And also, provably wrong using patents. Har.)

Irrespective of any discussion of the usefulness of this observation, some of the fact checking from the tech press has asked the wrong questions. (This really is a CDM story – just bear with me.)

First, can a microwave oven be used as a spying device? Answer: yes. In fact, not only can you use a microwave oven to eavesdrop on people, anyone with some basic electronic skills could build the system themselves. A 2005 article from EE Times shows you how (thanks, Jan Klug):

Eavesdropping using microwaves

This is literally (and now unintentionally hilariously) in the Design How-To section of the magazine. Apologies to any EE Times readers I’ve just gotten on a watch list. Hey, more time indoors to work on electronics projects, right? No?

Spying with microwave ovens is actually reasonably easy, because electromagnetic frequencies reflect physical vibrations – they become a carrier for sound. So even without a microphone, EMF signals can under the right circumstances contain the traces of sound waves as amplitude modulation. Microwave ovens are useful because they amplify that signal. Get close to someone using a microwave oven and hope they’re saying something useful while that microwave is on, and you can spy on them without needing to plant a device. (I don’t know this because I’m a spy. I know this because I read it in the EE story above.)

Now, this won’t come as news to anyone who’s a fan of the history of Leon Theremin, because the inventor of the instrument of the same name also pioneered the technique. I’ve actually shown his invention (The Bug) in lectures, because the story is just too good.

And anyone who’s met Theremin history expert Andrey Smirnov has surely heard the story, as he tells it frequently.

EE Times also credits Lev. But let’s just copy-paste from our friends as the United States NSA:

On August 4, 1945, Soviet school children gave a carving of the Great Seal of the United States to U.S. Ambassador Averell Harriman. It hung in the ambassador’s Moscow residential office until 1952 when the State Department discovered that it was ‘bugged.’

The microphone hidden inside was passive and only activated when the Soviets wanted it to be. They shot radio waves from a van parked outside into the ambassador’s office and could then detect the changes of the microphone’s diaphragm inside the resonant cavity. When Soviets turned off the radio waves it was virtually impossible to detect the hidden ‘bug.’ The Soviets were able to eavesdrop on the U.S. ambassador’s conversations for six years.

From a declassified 2007 NSA report

Beware of Soviets bearing gifts, apparently. This is doubly ironic, as I’d pondered before constructing one of these in a workshop or hacklab.

The key is the resonant cavity. It doesn’t require a power source, and it’s hard to detect, but you still have to plant the device. The microwave oven is advantageous because you don’t have to do that. The EE Times story is a great read, because it gives some history into patent applications around the concept – some of them unrelated to sound detection, looking instead to distance. (I’m told the AutoTune algorithm was first developed for seismic exploration, so remember that imaging and sound are connected.)

But that brings us to the next question:

Could a microwave be used as an imaging device? Here, the likely answer is – possibly, sort of, but it wouldn’t be your first choice.

Now, the couple of tech articles I read on this target may have asked too narrow a question. Given recent revelations that camera-equipped computers and smart TVs used the actual in-built cameras as hacking targets, they asked whether microwaves could be hacked in the same way. There, the answer is pretty definitively no, because there aren’t many microwaves with optical cameras facing outward.

But strictly speaking, can you definitively rule out the possibility of using a microwave as an imaging device? Probably not.

First, yes, there are ways of using electromagnetic radiation to produce an image. See the above technique, and think radar: if you can make a sound, you can make a picture, too. The trick is, you might wind up with a precise image of what someone had put in their microwave, at least using whatever conventional approaches I’ve been able to find. If some lumpen picture of last night’s Chinese take-out is your idea of vital surveillance, then you’ll be happy with this solution. But uh… yeah, that’s unlikely.

Of course, if your objective is spying, getting quality data is important.

But there could be other techniques. One friend pointed me to this:

Rosenthal Sensor [Eric Rosenthal, GitHub]

Conspiracy theorists, that involves DARPA (US defense funding) and New York City, not far from Trump Tower. But… okay, it’s actually not directly applicable to the microwave oven example. But it does prove that there are unique ways of making sensors, which means there are all sorts of unknowns here – and just talking about webcams and the Internet of Things isn’t sufficient.

That said, back to reality.

It’s one thing to say that a microwave oven could be used for surveillance. It’s another to say it’d be your first choice – or anywhere up the list.

The thing is, all of this becomes less appealing once you have loads of Internet-connected devices with sensors on them. And that’s to say nothing of the fact that it’s easy to compromise someone’s existing data simply by guessing their password, or waiting for them to make something public that was intended as private, or any other number of techniques.

But I think what’s more interesting than any of this is the fact that spying is all about doing something that the other person doesn’t expect. That’s what made Theremin a genius. He took a technique that was technologically simple and applied it to a new context, in such a way that no one had thought to look.

They didn’t ask the right questions.

And that’s fundamentally what science is about – asking questions, rather than assuming you have the answers.

By that measure, these articles failed, as did I with my initial kneejerk reaction. Thanks to Tessa Lena via Facebook for calling us out on that.

And I’d say culture is often about finding answers from entirely different questions – which is how the person who is the father of the modern electronic musical instrument is also the father of the modern surveillance state. I just hope, frankly, his weird-sounding music outlives all these other institutions.

With that in mind:

Meanwhile, if you want to learn electronics with the help of the NSA (your tax dollars at work, Americans!), here you go:

Homebrew NSA bugs

And… I’m not helping any of us get our DIY electronic instruments across national borders, am I? Sorry. (Maybe just wink knowingly at border crossing people and tell them they shouldn’t ask more questions, or some people higher up will be displeased. Actually, no, maybe definitely don’t do that.)

The post You could spy on someone using a microwave oven as a mic appeared first on CDM Create Digital Music.


Leave a Reply