Besides buzzing to alert you to calls, texts, and alarms, a phone's vibration motor can also function as a solid speech sensor, researchers have demonstrated.
And that means one more potential method for spies to eavesdrop on phone conversations, Nirupam Roy and Romit Roy Choudhury from the University of Illinois at Urbana-Champaign argue in a paper detailing their VibraPhone, a system designed to recover and distill words from currents transmitted by vibration motor circuits.
"We show that the vibrating mass inside the motor, designed to oscillate to changing magnetic fields, also responds to air vibrations from nearby sounds," the pair write.
That the motor did respond to sound wasn't surprising but they didn't expect it could be used to reproduce audible speech and thus act as a kind of microphone.
Besides eavesdropping, the researchers argue it could be used to enable voice control on devices that don't have a microphone, such as fitness trackers, and could be a fairly low overhead on battery power since it operates in passive mode.