How are smartphone accelerometer and gyroscope sensors used for covert tracking?

THEY READ KEYBOARD VIBRATIONS, STEPS, AND RECONSTRUCT SPEECH SOUNDS WITHOUT MIC ACCESS.

Mobile OSs often give sites and apps motion sensor access without explicit permission prompts. High-frequency measurements of phone body vibrations can reconstruct entered PINs and conversation context.

Analyzing Physical Device Body Vibrations

Motion sensors record micro-vibrations from phone speakers and finger taps on the screen. Advanced machine learning algorithms can accurately determine numbers typed on soft keyboards from body tilt angles, as well as pick up low-frequency acoustic voice waves from nearby people.

Neutralizing Covert Kinetic Tracking

disable web page access to motion sensors in browser privacy settings
restrict background activity for apps that don't need step tracking or navigation
avoid typing sensitive PINs and passwords while holding the phone in loud public places
prefer mobile browsers with built-in sensor polling rate limits