Matchstick-Sized Sensor Can Record Your Private Chats Outdoors

wabrandsma sends this story from New Scientist: "A sensor previously used for military operations can now be tuned to secretly locate and record any single conversation on a busy street. [A] Dutch acoustics firm, Microflown Technologies, has developed a matchstick-sized sensor that can pinpoint and record a target's conversations from a distance. Known as an acoustic vector sensor, Microflown's sensor measures the movement of air, disturbed by sound waves, to almost instantly locate where a sound originated. It can then identify the noise and, if required, transmit it live to waiting ears. Security technologist Bruce Schneier says this new capability is unwelcome – particularly given the recent claims about the NSA's success at tapping into our private lives. 'It's not just this one technology that's the problem,' Schneier says. 'It's the mic plus the drones, plus the signal processing, plus voice recognition.'"

Comments

Re:a few laws of physics problems here

[ebno-10db]

Governments have always had the technical means to be invasive, they are restrained by common decency and the law of the land.

They are?

If you want to set up a big acoustic array at the beach

Were I to surveil the beach, I'd be more interested in visual than auditory information. YMMV.

All joking aside, I'm skeptical of the technical claims of superiority, other than small size. That's tempered by my lack of knowledge of acoustics. I think of it in terms of analogies to optics or radar (as a physicist I once knew said, a wave is a wave is a wave). You need an array to locate the direction something is coming from. Roughly speaking the larger the array relative to the wavelength, the more precisely you can determine direction, and the more you can spatially filter that source from other sources. You can do that with small optical sensors (e.g. a camera or your eye) only because of the short wavelength of light. Radar antennas with the same directionality and resolution need to be much larger. At 1kHz (a frequency you definitely need to understand conversation) the wavelength of a sound wave is 343mm. For radio waves that's the wavelength you'd get at 875MHz. You need a fairly big antenna to get decent resolution. That can be accomplished by widely spaced sensors (antenna elements, whatever) and some serious signal processing. I don't see how one of these sensors can have any serious directionality by itself, or having three in the same place pointing at x, y and z directions can do much.

One difference I can think of between electromagnetic radiation and sound waves is that the former are transverse waves and the latter are longitudinal waves. Does that make much of a difference for these purposes?