How your smartphone's battery life can be used to invade your privacy

A group of researchers have demonstrated how to track users with nothing more than their remaining battery power, which could compromise privacy

A little-known feature of the HTML5 specification means that websites can find out how much battery power a visitor has left on their laptop or smartphone - and now, security researchers have warned that that information can be used to track browsers online.

The battery status API is currently supported in the Firefox, Opera and Chrome browsers, and was introduced by the World Wide Web Consortium (W3C, the organisation that oversees the development of the web's standards) in 2012, with the aim of helping websites conserve users' energy. Ideally, a website or web-app can notice when the visitor has little battery power left, and switch to a low-power mode by disabling extraneous features to eke out the most usage.