Smartphone barometer can hear, and sense finger taps

Area of Science:

• Mobile device security
• Sensor privacy
• Human-computer interaction

Background:

• Modern smartphones integrate barometers for air pressure sensing, typically accessed without user permission due to perceived harmlessness.
• Ingress protection in smartphones may inadvertently enhance the sensitivity of barometer data to internal acoustic and tactile events.

Purpose of the Study:

• To investigate the potential for smartphone barometer data to reveal sensitive user information.
• To assess the accuracy of using barometer readings to detect speaker activity and touchscreen interactions.

Main Methods:

• Utilized a support-vector machine (SVM) classifier to analyze barometer readings.
• Tested the system with low-frequency barometer sampling rates (25 Hz).
• Evaluated the classifier's performance in detecting speaker activity (silence vs. ringtone) and touchscreen finger taps.

Main Results:

• Achieved over 95% accuracy in distinguishing between silent and ringtone audio playback using barometer data.
• Demonstrated nearly 100% accuracy in detecting touchscreen finger taps.
• Showed that barometer samples can provide information on the approximate location of finger taps.

Conclusions:

• Smartphone barometers, contrary to common belief, are sensitive sensors that can leak private user information.
• Access to barometer data should be carefully managed to mitigate potential privacy breaches.
• The findings highlight the need for enhanced privacy controls for seemingly innocuous smartphone sensors.