In the age of surveillance paranoia, most smartphone users know better than to give a random app or website permission to use their device’s microphone. But researchers have found there’s another, little-considered sensor in modern phones that can also listen in on their conversations. And it doesn’t even need to ask. In a presentation at the Usenix security conference next week, researchers from Stanford University and Israel’s defense research group Rafael plan to present a technique for using a smartphone to surreptitiously eavesdrop on conversations in a room—not with a gadget’s microphone, but with its gyroscopes, the sensors designed measure the phone’s orientation. Those sensors enable everything from motion-based games like DoodleJump to cameras’ image stabilization to the phones’ displays toggling between vertical and horizontal orientations.