Apps that use your smartphone's microphone need to ask permission, but the motion sensors? No say-so needed. That might not sound like a big deal, but security researchers from Stanford University and defense firm Rafael have discovered a way to turn Android phone gyroscopes into crude microphones. They call their app "Gyrophone" and here's how it works: the tiny gyros in your phone that measure orientation do so using vibrating pressure plates. As it turns out, they can also pick up air vibrations from sounds, and many Android devices can do it in the 80 to 250 hertz range -- exactly the frequency of a human voice.

By contrast, the iPhone's sensor only uses frequencies below 100Hz, and is therefore useless for tapping conversations. Though the researchers' system can only pick up the odd word or the speaker's gender, they said that voice recognition experts could no doubt make it work better. They'll be delivering a paper next week at the Usenix Security conference, but luckily, Google is already up on the research. "This early, academic work should allow us to provide defenses before there is any likelihood of real exploitation."