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.