Mobile phones can track YOU using little-known battery life loophole
Security experts say smartphones give away details of their owners' online movements
Smartphones can used to track their owners by analysing the device's battery usage, tech security experts have warned.
A team from Princeton University found that websites could use battery information to monitor people as they surf the web.
Modern smartphone software sends data to internet pages so they can offer different pages when the battery is low and avoid draining it further.
But this same information could reveal tell-tale clues about the phone's owner.
Lukasz Olejnik, a security researcher, wrote: "Privacy risks and threats arise and surface even in seemingly innocuous mechanisms. We have seen it before, and we will see it again."
He suggested firms want to start buying access to battery life stats, which would allow them target people when they were vulnerable.
For instance, if someone uses a taxi app when their battery is low, they are likely to agree to pay higher fares so their car arrives before the phone stops working.
Olejnik added: "Some companies may be analysing the possibility of monetising the access to battery levels. When battery is running low, people might be prone to some - otherwise different - decisions. In such circumstances, users will agree to pay more for a service."
The revelations are already angering campaigners.
"Unfortunately, it is no surprise that battery levels are being used to track individuals," Dr Richard Tynan from Privacy International, .
"At face value, battery levels appear to be something that no one would or should ever spend time caring about.
"However we have seen companies gleefully exploit this seemingly mundane data that is generated as you use the battery in your device."
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