MEMS accelerometer

2 Articles

Your Phone Is Now Helping To Detect Earthquakes

August 17, 2020 by 37 Comments

Most people’s personal experience with seismographs begins and ends with simple childhood science experiments. Watching a pendulum make erratic marks on a piece of paper while your classmates banged on the table gave you an idea on how the device worked, and there’s an excellent chance that’s the last time you gave the concept much thought. Even among hackers, whose gear in general tends to be more technologically equipped than the norm, you’re unlikely to find a dedicated seismograph up and running.

But that’s not because the core technology is hard to come by or particularly expensive. In fact, one could say with almost absolute certainty that if you aren’t actively reading these words on a device with a sensitive accelerometer onboard, you have one (or perhaps several) within arm’s reach. Modern smartphones, tablets, and even some laptops, now pack in sensors that could easily be pushed into service as broad strokes seismometers; they just need the software to collect and analyze the data.

Or at least, they did. By the time you read this article, Google will have already started rolling out an update to Android devices which will allow them to use their onboard sensors to detect possible earthquakes. With literally billions of compatible devices in operation all over the planet, this will easily become the largest distributed sensor network of its type ever put into operation. But that doesn’t mean you’re going to be getting a notification on your phone to duck and cover anytime soon.

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This WAV File Can Confuse Your Fitbit

March 15, 2017 by 30 Comments

As the devices with which we surround ourselves become ever more connected to the rest of the world, a lot more thought is being given to their security with respect to the internet. It’s important to remember though that this is not the only possible attack vector through which they could be compromised. All devices that incorporate sensors or indicators have the potential to be exploited in some way, whether that is as simple as sniffing the data stream expressed through a flashing LED, or a more complex attack.

Researchers at the University of Michigan and the University of South Carolina have demonstrated a successful attack against MEMS accelerometers such as you might find in a smartphone. They are using carefully crafted sound waves, and can replicate at will any output the device should be capable of returning.

MEMS accelerometers have a microscopic sprung weight with protruding plates that form part of a set of capacitors. The displacement of the weight due to acceleration is measured by looking at the difference between the capacitance on either side of the plates.

The team describe their work in the video we’ve put below the break, though frustratingly they don’t go into quite enough detail other than mentioning anti-aliasing. We suspect that they vibrate the weight such that it matches the sampling frequency of the sensor, and constantly registers a reading at a point on its travel they can dial in through the phase of their applied sound. They demonstrate interference with a model car controlled by a smartphone, and spurious steps added to a Fitbit. The whole thing is enough for the New York Times to worry about hacking a phone with sound waves, which is rather a predictable overreaction that is not shared by the researchers themselves.

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