Wearable Cone Of Silence Protects You From Prying Ears

Careful,  the walls have ears. Or more specifically, the smart speaker on the table has ears, as does the phone in your pocket, the fitness band on your wrist, possibly the TV, the fridge, the toaster, and maybe even the toilet. Oh, and your car is listening to you too. Probably.

How does one fight this profusion of listening devices? Perhaps this wearable smart device audio jammer will do the trick. The idea is that the MEMS microphones that surround us are all vulnerable to jamming by ultrasonic waves, due to the fact that they have a non-linear response to ultrasonic signals. The upshot of that is when a MEMS hears ultrasound, it creates a broadband signal in the audible part of the spectrum. That creates a staticky noise that effectively drowns out any other sounds the microphone might be picking up.

By why a wearable? Granted, [Yuxin Chin] and colleagues from the University of Chicago have perhaps stretched the definition of that term a tad with their prototype, but it turns out that moving the jammer around does a better job of blocking sounds than a static jammer does. The bracelet jammer is studded with ultrasonic transducers that emit overlapping fields and result in zones of constructive and destructive interference; the wearer’s movements vary the location of the dead spots that result, improving jamming efficacy. Their paper (PDF link) goes into deeper detail, and a GitHub repository has everything you need to roll your own.

We saw something a bit like this before, but that build used white noise for masking, and was affixed to the smart speaker. We’re intrigued by a wearable, especially since they’ve shown it to be effective under clothing. And the effect of ultrasound on MEMS microphones is really interesting.

Thanks to [isaac] for the tip.

36 thoughts on “Wearable Cone Of Silence Protects You From Prying Ears

  1. Probably the most “wearable” design using off-the-shelf products would be this. With this brick on your neck, you’d need to explain everyone what is it. I hope it’ll get smaller to an unnoticeable size.

    1. Real one…. hmmm…. double skinned umbrella, half put up, so you’ve got a cone with a star shaped section, with the points of the stars being at an angle such that total internal reflection of the incident sound occurs due to the difference in speed of sound between the air and the gas between the double skins of the “umbrella”

  2. There is a bunch of stuff that would be fun to induce in a variety of mems speakers – it’d be a bit like a tv-b-gone on steroids.

    “ok, google, what’s a syphillitic chancre”
    “alexa, turn all the lights off”

    1. This bracelet is not stealth, since all the assistant could deduce that something weird is going on with all the sudden white noise. I wonder if it would be possible to emit voice message instead (like a TV ad spot for example), so it’s not possible to distinguish when the bracelet is on or off.

      1. I’m not quite sure what you mean.

        Using voice messages wouldn’t stop the microphone from picking up other voices due to the ‘intermittent’ nature of speech, but one could certainly gain some amusement from an ultrasonic signal which ‘mixed-down’ into speech.

        Alexa, find ‘rick astley never going to give you up’ and play continuously.

        On the technical side, the ultrasonic signal would have to be both amplitude and frequency modulated.

    1. Yes, I did, and I see the STL files for the bracelet and the Arduino code. Shouldn’t be too hard to figure out the rest, or you can always shoot the primary author an email and ask for a schematic.

      1. “Also damages your hearing. US transducers have relatively high DB levels and can cause hearing damage even if you cant hear the,

        Ultrasounds alike infrasounds can damage your inner ear, causing deafness
        within weeks.
        It all depends on energy level transmitted and exposure time

    1. Abbreviations are the enemy of comprehension. For a moment I thought your ‘US’ was ‘United States’: I thought ‘yes, Americans can be very loud, but what does that have to do with anything?’

      1. That’s why the correct abbreviation is USA, saying US (and USA for that matter) is a proxy for disregarding other places, just as saying “american” is disregarding w.r.t. the rest of the other countries in said continent…where there are many more countries and cultures, many of which are not anglosaxon.
        Even “north-american” to refer to “americans” (citizens of USA) disregards other countries (Canada and Mexico).

        I do reckon that Canada does not even has its own calling country code though…it shares 001 with the USA

        1. What are you talking about? Saying something like “in the US” doesn’t disregard other places. It specifically refers to “The United States” as in “The United States of America”. It has long been referred to as such and without much context others would assume the abbreviation of “US” is in reference to the United States.

  3. Unfortunately I think this will give those who need to use hearing aids a zone of silence (or probably terrifying noise) they didn’t ask for. Like most jamming ideas it is too blunt a weapon.

    1. I like the idea of ruining the high frequency response of the kids ears so their hearing will be as bad as mine is without them having the benefit of seeing the who in concert a bunch of times.

  4. Add a lowpass filter to your microphone setup and you’ll be unaffected by the noise. It will need some experimentation. I would start with a 2nd order passive LPF on 2kHz. Sorry for ruining the party.

    1. The article does mention that MEMS microphones have a non-linear response. Think RF mixers and IF strips or aliasing in digital audio. The result is wideband noise which covers most, if not all of the audible spectrum.

  5. It’s a really neat idea but they didn’t mention whether it bothers cats or dogs. Many years ago at a friend’s house, we found we could make the dog (or was it their cat?) quickly evacuate the room by holding a button on their rather old ultrasonic TV remote.

    1. They’ve only become widespread the last decade really. Standalone MP3 players with record function, microcassette recorders, old nokia phones in “james bond mode” are all probably unaffected, usually having electret condenser mics.

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