Smartphones can be tracked via power usage

Malicious software can track your smartphone simply by measuring the way it uses power even without access to location data, scientists warn.
The technique is based on the idea that a smartphone's power usage depends largely on the distance from the nearest base station.
As a user moves, this distance changes, increasing or decreasing the power needed to communicate with a base station.
The power usage profile is strongly correlated with the movement of the phone, or in other words, with the route taken by its owner, according to MIT Technology Review.
Given several different potential routes, the power usage profile should show which route the user has taken.

"Our approach enables known route identification, real-time tracking, and identification of a new route by only analysing the phone's power consumption," said Yan Michalevsky at Stanford University in California and colleagues.

For the idea to work, the user must be moving as power usage profile is no use in identifying the location of a stationary phone.
To find out how well this technique works in practice, the team created an Android app called PowerSpy that measures power usage.
They then tested it on a number of devices. In total, they took 43 different power usage profiles on four different routes each about 14 kilometres long.

Researchers could determine which route had been taken with an accuracy of 93 per cent just by analysing the power usage profiles.
"We showed that applications that read the phone's ampere meter can gain information about the location of a mobile device without accessing the GPS or any other coarse location indicators," they said.