
Wearable Microphone Jamming - RandomGuyDTB
http://sandlab.cs.uchicago.edu/jammer/
======
VectorLock
Would this hurt people with cochlear implants?

~~~
rahuldottech
Yes.

> _Yikes, please don 't do or encourage using these in public - there are many
> accessibility devices (hearing aids, cochlear implants, etc.) which depend
> on MEMS microphones to function._

> _You could inadvertently make the world much worse for people who already
> have a difficult time of things. Imagine carting a cellular and WiFi and
> bluetooth jammer around outside of a Faraday cage - it 's insanely
> irresponsible and inconsiderate. _

From the top comment here:
[https://news.ycombinator.com/item?id=22339548](https://news.ycombinator.com/item?id=22339548)

~~~
nonbirithm
It would be a loss if due to a critical need to protect privacy we end up
inadvertently harming a group of people that are already at a disadvantage. I
once knew a hearing-disabled person and the hardship it brought them affected
nearly every interaction with them I had. For me that trade-off is not worth
it.

If the best channel to help the deaf listen clearly is also the best one for
letting eavesdroppers listen clearly, then this is a problem best not handled
with such a heavy handed solution - possibly not even a technological solution
at all.

~~~
inetknght
> _It would be a loss if due to a critical need to protect privacy we end up
> inadvertently harming a group of people that are already at a disadvantage.
> I once knew a hearing-disabled person and the hardship it brought them
> affected nearly every interaction with them I had. For me that trade-off is
> not worth it._

We already do this by making so many things practically require internet
access but then also not making things easily accessible to eg screen readers
or text mode browsers

~~~
vages
Norway, where I live, has enacted laws banning inaccessible websites (with the
exception of websites made by individuals). [https://medium.com/confrere/its-
illegal-to-have-an-inaccessi...](https://medium.com/confrere/its-illegal-to-
have-an-inaccessible-website-in-norway-and-that-s-good-news-for-all-of-
us-b59a9e929d54)

The law has been well-received both by the public and by businesses, with very
few actual fines being issued, but many bad pages have been soft-forced into
improvement. So it's actually possible, but will probably be much harder in
the US, in which business, government and taxpayers/customers seem less
aligned.

------
squarefoot
The interesting parts are those 25KHz transducers which seem identical to the
40KHz used since likely forever in ultrasound remotes and more recently in
collision avoidance sensors for robotics. I did a small search and found
mostly high powered ones at that frequency, probably ultrasound cleaners
spares, or smaller but a lot more expensive transducers compared to 40 KHz
ones. Does anyone know of a source for these transducers?

I also wonder if a simpler approach could be used since the purpose appears to
be (can't understand the math) generating noise by driving randomly a number
of oscillators around the transducers resonance frequency then induce
subharmonic vibrations into the MEMS mics through etherodyne operations
between these sounds. If that's how it works, then the DDS chips, the Arduino
and the code might be swapped with a less random but likely equally functional
set of dissonating oscillators modulated by LFOs (all doable with plain old
logic gates); not unlike the old school way of generating cymbals metallic
sound in analog drum machines. Here's the Boss DR110 relevant schematic as an
example.

[http://www.sdiy.org/richardc64/new_drums/dr110/dr110a1.html](http://www.sdiy.org/richardc64/new_drums/dr110/dr110a1.html)

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sigstoat
the original paper on jamming microphones and/or using them for covert data
transmission:
[https://synrg.csl.illinois.edu/papers/backdoor_mobisys17.pdf](https://synrg.csl.illinois.edu/papers/backdoor_mobisys17.pdf)

it seems to me that this is largely an attack on common preamplifier
circuitry. would it be sufficient to ensure that the preamps implement low
pass filtering? or is the issue more in the microphone element?

~~~
neetdeth
From the paper linked:

"For the above idea to work with unmodified off-the-shelf microphones, two
assumptions need validation. (1) The diaphragm of the microphone should
exhibit some sensitivity at the high-end frequencies (> 30kHz). If the
diaphragm does not vibrate at such frequencies, there is no opportunity for
non-linear mixing of signals."

The devices tested include hearing aids, smartphones, smart watches, etc,
which are all likely to include small surface mount MEMS microphones. I doubt
any of these techniques will work against a larger dynamic or condenser
microphone, where the mass of the diaphragm makes the system inherently
insensitive to ultrasonic frequencies. There's a reason the jamming signal is
inaudible, and it's not because our auditory cortex contains an ideal lowpass
filter.

~~~
sigstoat
Yes, I agree that the microphone has to be responsive to ultrasound. That
doesn't seem to be the only requirement, though:

"When these tones arrive together at the microphone’s power amplifier, they
are amplified as expected, but also multiplied due to fundamental non-
linearities in the system"

"In practice, however, acoustic amplifiers maintain strong linearity only in
the audible frequency range; outside this range, the response exhibits non-
linearity."

That suggests to me that the nonlinear mixing isn't occurring in the MEMS
structure, but rather the amplification stage. Perhaps the authors' language
is imprecise?

They do say immediately after the last bit:

"The diaphragm also exhibits similar behavior [non-linearity]."

Is just the diaphragm's nonlinearity sufficient for the effect?

~~~
neetdeth
Ok, that's actually a lot more interesting than I was giving them credit for.
I assumed they were just overwhelming the LPF or exploiting some side lobe to
create aliasing in the audible range, but that's discussed in section 2.

All I can contribute is that nonlinearity in audio systems is also known as
distortion, and it's impossible to eliminate entirely because every system,
whether electrical mechanical or even digital, goes nonlinear when it reaches
its amplitude limits. Some more gracefully than others.

Seems like it would be difficult to tease out the relative contribution of the
MEMS element and the preamplifier because the preamps are typically
implemented on ASICs in the same package. So that might be speculation on the
authors' part.

------
vorpalhex
This is really neat work. I'm curious to see if smaller and more portable
versions of this can be made - obviously a prototype is always going to be
bigger and be relatively limited. Now that the research has been surfaced,
this appears easy enough to follow so it'd be neat to see how electronics
enthusiasts run with it.

~~~
ct0
Do cell phone speakers operate at this frequency range as well? I could
imagine an app specifically focusing on responding to the words "to be safe",
by turning on the white noise maker.

~~~
rtkwe
Ironic.. to destroy the always listening app we propose a different always
listening app to jam.

------
bmgxyz
I think this is a neat idea, but I suspect it would be more useful as a
standalone device than as a wearable. Devices like this could be installed in
secure rooms or deployed on the fly in discreet locations with a high rate of
success, I'd guess. Arrays of them could work together for better coverage.

Still, this may be the only real option in public spaces (i.e. outdoors). If
you're okay with people knowing that you're trying to avoid being recorded,
then this would probably be fine.

~~~
tsumnia
I envision a variation that sits in the corner of a room, similar to how a fan
operates, gradually turning the speakers. However, as others mentioned, I'm
curious over the effect it would have on hearing aids, etc. Secondly, if there
a variation of this device that could straight up disable WiFi?

~~~
BeefySwain
Jamming wifi (as well as many (most?) other frequency bands) is very simple
and very illegal.

[https://en.wikipedia.org/wiki/Radio_jamming](https://en.wikipedia.org/wiki/Radio_jamming)

~~~
tsumnia
Right, that'd be my concern - that if their implementation could be modified
in a similar manner to create jammers that would be quick to deploy but
difficult to locate.

------
mdszy
Sure it's "wearable" if your definition of "wearable" is incredibly loose.

~~~
__ryan__
It's only "wearable" if your definition of "wearable" doesn't take into
account style. I mean, come on! The space age design wouldn't pair well at all
with my wardrobe. Can you imagine that clunky thing over the cuffs of my Ralph
Lauren suit jacket? Rating: 0/10\. under no circumstances would I don that
monstrosity.

Edit: sorry, I went against my better judgement and decided to respond
sarcastically to the other comment. I was being facetious.

~~~
diego_moita
Are you both sure you understand the difference between the terms "proof of
concept" and "final product"?

~~~
mdszy
I'm sure of exactly zero things.

~~~
kempbellt
You sure about that?

~~~
mdszy
Nope!

------
asdfman123
I can see this being useful for blocking your smartphones and Alexas, but it
seems like devices specifically designed for surveillance could start being
designed to fix this exploit.

------
wadkar
How will this impact calls? If somebody is wearing this in a public space then
any callers in surrounding area will have problems, no?

It would be interesting to evaluate this device’s impact on telephonic
conversation!

I hope there is a switch to turn the device on/off. Otherwise you won’t be
able to talk on the phone :-)

~~~
devb
It's already been tried!

"During a phone interview, Mr. Lopes turned on the bracelet, resulting in
static-like white noise for the listener on the other end."

[https://www.nytimes.com/2020/02/14/technology/alexa-
jamming-...](https://www.nytimes.com/2020/02/14/technology/alexa-jamming-
bracelet-privacy-armor.html)

------
kylek
What could go wrong with blasting out ultrasonic noise in every direction?
(Besides a lot of confused dogs...)

~~~
LinuxBender
Starving bats. Bats keep moth and mosquito populations down in some areas.
They use ultrasonic acquisition of their prey.

Rodents less likely to nest near you may be a positive thing.

~~~
m463
Great story here:

 _he said, "Watch the moths." It turns out the moths, through evolution, had
developed their own electronic countermeasures to jam the bat radar_

[https://steveblank.com/2009/03/23/if-i-told-
you-i%E2%80%99d-...](https://steveblank.com/2009/03/23/if-i-told-
you-i%E2%80%99d-have-to-kill-you-the-story-behind-the-secret-history-of-
silicon-valley/)

------
falcolas
Another discussion of this:
[https://news.ycombinator.com/item?id=22339548](https://news.ycombinator.com/item?id=22339548)

------
alasdair_
A similar effect occurs when using infra-red LEDs near the face to prevent
video recording. The problem is that many phone cameras now have a UV/IR
filter - I can see microphones having a similar setup to improve sound quality
in the future.

~~~
elric
All CMOS cameras have an IR filter, for reasons that have nothing to do with
people using IR LEDs to fool (some) cameras. In fact, removing the IR filter
and replacing it with a visible light filter is a cheap way to turn a cheap
webcam into a (crappy) night vision camera.

------
fyz
This might result in jammed audio for human listeners, but recovering the
original audio seems like a fairly mundane signals extraction problem subject
to the standard signal/noise ratio issue.

------
btbuildem
Is sound of that frequency naturally directional? Wonder if an omnidirectional
driver / sound source could be used to prevent the "dead spots"

------
shanxS
Can someone please explain what is stopping these recording devices
(Alexa/phone/etc) to filter out ultrasound?

~~~
stefan_
As I understand it, they of course already filter it out, but filters are
imperfect and it bleeds in at the cutoffs or aliases.

~~~
shanxS
I see, so it's matter of time before off-the-shelf microphones become
technically advannced enough to counter this.

~~~
moftz
It's not an advancement thing, its a cost thing. They made the filter good
enough to block out the stuff people can't hear but this device is super loud
so you would need additional layers of filtering to completely block it.
Smartphone mics need to be tiny so additional analog filtering is going to
take up space and resources. You could also run a higher sample rate on the
ADC that converts the sound to a digital signal and run a digital filter to
cut off the ultrasonic band but that requires more power and chip resources
and the ADC might need to be swapped for one capable of the higher sample
rate. The tools are all there to defeat this but it's a matter of reducing
power, cost, and computing resources.

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kbumsik
> The leakage is caused by an inherent, nonlinear property of microphone’s
> hardware.

Interesting, what are related theories I can learn about it deeply?

~~~
jasonwatkinspdx
[http://www.gedlee.com/Books/AudioTransducers.aspx](http://www.gedlee.com/Books/AudioTransducers.aspx)

------
villmann
Won't somebody please think about the dogs

------
annoyingnoob
The world is in a sad state of affairs when smart people feel the need to
create wearable jamming devices.

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lovetocode
And this is also likely very illegal...

~~~
Polylactic_acid
Would it? I'm not aware of any laws about sound that wouldn't bother the human
ear. The closest thing I can think of is laws about RF jamming but this
clearly isn't a radio frequency.

~~~
stubish
Hearing aids, emergency telephones and phones used by medical and security
personnel are already covered by laws in many places. Also messing with law
enforcement devices, like police body cams. The people developing this could
technically be liable right now if they tested the device in a public space.
It will never get as far as the University library. The main use of this
research will be in selling better mikes to the military and police.

------
closetohome
It seems a little irresponsible for an academic publication to make a claim
like

> always listening, recording, and possibly saving sensitive personal
> information

without any evidence to support it. I get that they're just setting up context
for their device, but they're also making some pretty serious (and widely
disproven) accusations.

~~~
kbumsik
> ... and possibly saving sensitive personal in- formation [32, 55, 38, 26].

They left 4 related articles in the publication please read the actual paper
before criticizing it.

> and widely disproven

I personally never heard of it. Any evidence?

~~~
closetohome
All of these devices have been reverse-engineered and packet sniffed to death,
and no one has ever produced any evidence that they're doing anything other
than what it says on the box.

While I do appreciate that the cited sources in their paper, I would have
appreciated actual information security papers rather than mainstream media
articles.

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phyzome
I would think this would function better as a hat than a bracelet.

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frandroid
Stylish!

------
biggrady
fuck dogs amirite

