Battery power alone can be used to track Android phones

A smartphone uses more power the further away it is from a cellular base and the more obstacles are in its way as it reaches for a signal. Additional power use by other activities could be factored out with algorithms, the researchers found.
They created an app designed to collect data about power consumption.
"The malicious app has neither permission to access the GPS nor other location providers (eg cellular or wi-fi network)," the team - Yan Michalevsky, Dan Boneh and Aaron Schulman, from the computer science department at Stanford University, along with Gabi Nakibly, from Rafael Ltd - wrote in their paper.