Researchers are investigating an important question: can cybercriminals record speech via smartphone motion sensors?

University of Alabama at Birmingham researchers suggest low-frequency radio signals, like human speech, within motion sensors like accelerometers and gyroscopes may present security flaws. These sensitives can allow cybercriminals to gather confidential data as the users speaks into or near a mobile device.

"These motion sensors are readily available in smartphones and other smart wearable devices that have become a predominant feature in everyone's life," says Nitesh Saxena, Ph.D., associate professor in the UAB College of Arts and Sciences Department of Computer Science.

"Unlike with microphones, users do not have to give newly installed applications permission to use them, making these sensors prime tools for malicious activity. This body of research is incredibly important to help protect users from myriad real and hypothetical privacy invasions," Saxena adds.

Stereo, laptop, and smartphone speakers, along with live human speech, were tested at different volumes during the researchers’ threat analysis. The team was studying the audio signal effects on a smartphone in varying locations: on the same surface as the speaker, on a different speaker, and through the air.

The results recorded an accelerometer change when the motion sensor and built-in laptop speakers shared the same surface. Stereo speakers showed similar findings, while smartphone speakers and human speech did not have enough power to register a response via aerial vibrations.

"In light of recent research and resulting news articles about the potential threat of smartphone motion sensors, the public perception is that this threat is very serious and motion sensors could record in the same way that a microphone does," says Doctoral Student Abhishek Anand. "Our research indicates that this is not the case. Motion sensors are very much limited in their capability of picking up speech characteristics. It is not possible for an accelerometer or gyroscope to act in the same capacity that a microphone does."

In the end, the research team found loudspeakers impacted the sensors mainly through shared conductive surfaces. However, human speech traveling through the air wasn’t powerful enough to cause an effect.  

“Overall, our results suggest that smartphone motion sensors may pose a threat to speech privacy only in some limited scenarios,” according to the researchers.

Read the article, “Speechless: Analyzing the Threat to Speech Privacy from Smartphone Motion Sensors,” published at the 2018 IEEE Symposium on Security and Privacy (SP), to learn more.