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Comment by S_A_P | Hacker News Reader

Maybe I am a bit dense here, but how does battery drain map to a location? What would they be cross referencing to gather location?

All I can gather is that they would also need to know what tower you were talking to, and then based on the drain they could probably guess where you were based on some heuristic. Meaning, if you are talking to tower x, and the battery drain is high, you could guess that you are either far from the tower or indoors somewhere. It still seems to me that this is dubious at best. I get that technology is always changing, but wouldn't it just be easier to exploit a security hole?

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As you move, your distance to the closest cell tower changes. You also move past signal obstacles, so the change in signal strength isn't linear. They claim that these changes are characteristic enough that you can track movement that way.

I get that part and to some degree understand. Maybe I am misinterpreting the "track your location" as something more accurate than "this person is in a 10 mile radius of this tower". For instance, wouldn't you need to know details of how different buildings are constructed? If you are in a busy downtown area, tracking with this method seems impossible. I could see if it was a remote area with few buildings to sift through.

Yes, it's not as trivial as just grabbing the data and running a generic algorithm. Ideally you would want to measure all routes where you want to track people. Kind of like how google knows where every wifi access point is and uses that for location information.

Also, you need people to move. Because you only have power data, you only know the aproximate signal strength if the person isn't moving.

That makes more sense. So to me, the headline reads as "Location can be tracked just by measuring battery usage" when in reality its "Location can be tracked if: A) they know the tower you are speaking to B) they have information on how buildings are constructed in this area C) You move around D) they have some other crowdsourced info about how much power is required to talk to the tower you are connected to."

I can see this "technique" being used in an episode of NCIS, CSI or similar cop show. <plot> We need to find this guy, but all we have is his cell number.

Police tech #1 "Sure no problem, I will just connect to his phone and measure the battery drain..... Got him, he is Downtown at 5th and Main- lets go arrest him!!!" </plot>

The article links the article where the authors suggest they don't need to know which tower you're connected to (in which case you could get a more accurate location from the towers themselves).They assume the only information you have from the phone is the power usage. However, they also assume the attackers have a general idea of your habits, and can therefore map out cell reception in the city where you live.

The "general habits" assumption seems implausible, but it isn't. Let's say you want to track all the citizens of the Bay Area. You know that, in general, ppl from the Bay area are in the Bay Area. Therefore, you map the cell reception in Bay area. You also take note of major transportation routes and patterns. Now, if you want to track a particular target, all you'll need is their power usage.

> For instance, wouldn't you need to know details of how different buildings are constructed?

They learned the typical profiles of power use for different journeys and then tried to distinguish between them (at least in one experiment).

http://arxiv.org/pdf/1502.03182v1.pdf

I don't know the specifics, but if I were to implement this I would start by constructing a signal map of an area, then comparing the signature of changes to potential routes.

By having a sufficiently accurate map, you could determine the likelihood of a route by the changes in signal. Even without pre-mapping there are some estimations that could be made: a signal that follows a clean sinusoidal curve with a certain rate of change could likely be modeled by rural highway driving.

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