Study finds 234 Android apps use ultrasonic tracking via microphone access

BOSTON — Researchers have identified 234 Android applications that capture inaudible sound signals above 18 kilohertz through users' microphone permissions, a tracking method known as ultrasonic cross-device tracking. The technique works by embedding high-frequency signals in advertisements, television broadcasts or in-store speakers that the human ear cannot hear. Smartphones pick up these signals and match them across a single user's television, computer and tablet, linking devices without their awareness. The findings build on a 2024 leaked Cox Media Group presentation that claimed smart devices could collect real-time intent data from user conversations. Google removed Cox from its partner program over the claims, Amazon denied the allegations and Cox said the documents were outdated. Separately, researchers at Northeastern University reviewed 17,000 Android apps and found none that recorded audio directly, though some covertly transmitted screenshots to third parties. Combined with location data, browsing history, loyalty card purchases and tools such as Facebook Pixel, the ultrasonic signals can contribute to highly detailed user profiles. Experts advise users to review microphone permissions, disable personalized advertising, turn off smart TV tracking services and delete Alexa and Google voice activity records.