Are you wary of giving apps permission to use GPS to locate your phone? Well, they may know where you are anyway by measuring small changes in your battery power according to a new study from Stanford University and researchers working for defense contractor Rafael.
A mobile phone uses more battery power the further away it is from a cellular base and the more obstacles there are blocking the signal as it tries to connect. The researchers designed an Android app to measure these changes in battery use which over time allowed them to locate phones with up to 90 percent accuracy.
The study used an app called PowerSpy but this battery use data can be gleaned from more than 179 apps available on the Google Play store including such seemingly innocent games like Angry Birds. The scary part is that unlike GPS and Wi-Fi, apps do not need to ask the user's permission to access battery use data.
"This information is considered harmless and reading it requires no user permission or notification", the study states. "We show that by simply reading the phone's aggregate power consumption over a period of a few minutes an application can learn information about the user's location."
Battery usage does of course fluctuate depending on how many apps are running on the device but the researchers were able to differentiate this type of power consumption as "noise" using machine learning techniques.
"Intuitively the reason why all this noise does not mislead our algorithms is that the noise is not correlated with the phone's location," said the report.
The one comfort is that this technique is not nearly as accurate as using GPS or Wi-Fi and can only really work when there is prior knowledge of the user's preferred routes. Researchers pre-collected data on seven different driving routes around California and Haifa in Israel. Then based on the battery data collected from an LG Nexus 4 Android phone they were able to identify which of the seven routes it was travelling 90 percent of the time.
So, Android users don't need to panic just yet. This technology alone isn't going to allow anyone to pinpoint a stranger's location but it could be used to track the locations of someone whose movements are known. It could presumably be of use to law enforcement agencies tracking the movements of known criminals.