Your Hard Disk As An Accidental Microphone

We’re used to attaching peripherals to our computers, when we have a need for them to interact with the world around them. An Arduino Uno needs a shield to turn on the lights, for example. Just sometimes though there is the potential for unintended interaction between a computer and the real physical world which surrounds it, and it’s one of those moments that [Alfredo Ortega] has uncovered in his talk at the EKO Party conference in Buenos Aires. He demonstrates how a traditional spinning-rust computer hard disk interacts with vibration in its surroundings, and can either become a rudimentary microphone, or be compromised by sound at its resonant frequency (PDF).

It seems that you can measure the response time of the hard drive head during a read operation without requiring any privilege escalation. This timing varies with vibration, so can be used to reconstruct the sound that the drive is facing. Thus it becomes a microphone, albeit not a very good one with a profoundly bass-heavy response. He goes on to investigate the effect of sound on the drive, discovering that it has a resonant frequency at which the vibration causes it to be unreadable.

Sadly the talk itself appears not yet to be online, but given that previous years’ EKO talks are on YouTube it is likely that when the dust has settled you will be able to see it in full. Meanwhile he’s posted a video demonstration which we’ve posted below the break.

Via [The Cybergibbons].

30 thoughts on “Your Hard Disk As An Accidental Microphone

  1. After a certain point in education regarding amateur radio and self study of TS/ES/RINT/SIGINT/EW… seems anything that has a resonance frequency will have a combination and difference frequency. Therefore, the sensitivity, accuracy and magnification of the signals receiver as well as the filtering (noise filtering, inverse background signal subtraction, etc.) is what is going to make a difference. I may be off a little. Still… seems. The strangest is the St. Louis arch being a resonator.

    I recall even the Weather Channel agreeing though am not finding a reference online yet. Kind of like my theory that I haven’t read anywhere that many of the Worlds particle accelerators are huge antennas and receivers or at least have the capabilities to be.

    Is the article also something like this article if you have some sort of classified system that can hypercritically tune for extremely specific resonant frequencies?

  2. “spinning-rust” no that’s not nice to say that…
    we don’t call solid state disks “expensive sand” or do we?
    A little more respect for the trusty hard drive, this thing has served us (and is still serving most of us) for many years and most likely for many years to come.

    PS: interesting effect

    1. I’m not so sure about the many more years. SSD technology is progressing very quickly and while still in it’s infancy compared to traditional mechanical hard drives it’s bound to replace it sooner than later. :(

      1. We still have magnetic tape storage. Tape storage is still improving. While gamers may think SSDs is the cure-all in the real world HDDs will not be replaced soon. SSDs have the advantage of low latency but are expensive and have lower effective storage density. There are still ways to improve storage density.

        Current solid storage (that aren’t disks) have already hit a fundamental limit that is hard to pass (flash memory can’t be shrunk efficiently anymore) which means that techniques like 3D stacked memory cells have to be used. But that is just a temporary solution, one can’t economically increase the number of layers too much and even if one could there would be problems with signal quality etc.
        Future solid storage will most likely shift to one of the alternative memory technologies like MRAM (magnetic storage) but nobody have succeeded in matching the density and performance of flash yet.

        TL;DR if you mean SSD as non-volative RAM then it’s in its middle-age, if you mean the flash based storage of today then it’s getting ready for the grave.

      1. Nope. Someone using the well known description is someone that uses that expression. IMO one shouldn’t listen to someone that thinks research is useless.

        Spinning rust is actually a good description of early HDDs (~60’s technology) that did indeed use a layer of iron oxides (=rust) that did indeed spin attached on mechanical support platters. It isn’t a good description anymore.

        Most people using it doesn’t understand how advanced modern magnetic storage is and how it (together with semiconductor industry) it have pushed technology forwards – not only in microfabrication, material science, application of and development of new sensors etc. but also in understanding how to to manage errors theoretically and practically.

          1. But is it stored by the molecules or just by some electromagnetic standing wave in a particular pretzelly twist, in a particular orientation, that we make believe are orbits of physical particles just to wrap our ape brains around and put in terms of real trees and fruit.

  3. Seismic laser ftw. Interesting PoC though and definitely a funny security hole. Kudos Alfredo!
    Really, a shield for the arduino to turn on lights? Mine did fine with a relay straight to pins. I guess maybe for multiple lights or something.

  4. If they are sensitive to vibrations, what about using hard drives to detect earthquakes.. Build a module into an operative system or some other widely distributed software and have it report back synchronized vibration.

    1. Hey yah, and we can have massively networked hard drive gravitic anomaly detectors and, particle detectors if everyone’s RAM is cross referenced, and phase switch everyone’s wifi to shoot down UFOs.

    2. ehmmmm… a microphone and a seismic device are not the same kind of devices just because they can detect virbrations. Although the idea of a huge network of countless computers creating a mesh of sensors sounds appealing, I have do not think that a harddrive is a suitable device for these kind of measurements.
      But the thought is interesting, simply by the number of “sensors” that could be involved.
      The problem of noise caused by humans surrounding the computers can be solved by comparing the noise measured by other computers in the mesh, if the noise is common, then it is most likely not noise but a real seismic signal.

          1. Incidentally, that would only be needed in 1 specific country of course.
            Problem is that if they used that method the hackers of that one country would soon find out about it from documents they stole.Unless they use the new method of letting the German BND do their bidding so it would possibly fly under the RADAR of such hackers.

    3. Earthquake detection using HDD is not a new idea, I remember reading about it when I was younger. But instead of using the read speed to detect vibrations (if I understood this article correctly), they wanted to use accelerometers already present in HDDs of laptops.

      Basically, there are accelerometers in some HDDs to detect freefall or shocks. When freefall is detected, the HDD can park the read head and avoid hitting the platter. If I recall correctly there was even a little icon on the taskbar of my father’s laptop indcating if the read head was parked or not due to a shock.

      I found some articles about it (probably the ones I read ten years ago):

      The website cited in the first article seems to still be up and running:

      There is even an article from Analog about freefall and shock detection in HDDs:

      So, I don’t think that you would even need to analyse the read speed to detect earthquakes if you can directly access the accelereometers. However, as far as I remember, on my father’s laptop you could only know if there had been a shock or not: this would only allow you to detect earthquake and not analyse them more precisely (which would be possible your method)
      In the end, it really depends on what kind of data you have access to :)

      (BTW, first comment on HaD :) )

  5. The sound frequency range needed to resonate a hard drive – – Is it anywhere close to the low-frequencies suspected to be the cause of injuries to diplomatic staff in Cuba?

    If Cuba was an attempt to read data from HDs using sound waves, would that explain a few things?

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