Stealthy Voice Eavesdropping with Acoustic Metamaterials: Unraveling a New Privacy Threat

2025-01-25

AI Summary

This work identifies a novel outdoor privacy threat: covert eavesdropping on smartphone earpiece acoustic leakage at distances up to 4.5 meters, enabling reconstruction of ~80% of spoken content with high intelligibility. To address this, we propose SuperEar—the first long-range, covert eavesdropping system targeting dynamic, mobile targets. Our approach integrates three key innovations: (1) a lightweight acoustic metamaterial array that enables physical-layer sound focusing and directional coupling; (2) a signal amplification and distortion-suppression reconstruction algorithm that overcomes inherent limitations in low-frequency gain and speech fidelity; and (3) the first real-time, portable implementation capable of tracking and eavesdropping on non-cooperative, distant, moving targets. Experimental results demonstrate a 20× amplification of speech amplitude and an end-to-end eavesdropping accuracy exceeding 80%, confirming practical feasibility for outdoor surveillance and tracking.

Technology Category

• Machine Learning: Privacy
• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems
• Computer Vision: Motion & Tracking

Application Category

• Security and Privacy: Large-scale security measurements
• Systems and Infrastructure for Web, Mobile and WoT: Energy management for devices in mobile Web and WoT environments
• Responsible Web: Data and user privacy-enhancing technologies for the Web

Abstract

We present SuperEar, a novel privacy threat based on acoustic metamaterials. Unlike previous research, SuperEar can surreptitiously track and eavesdrop on the phone calls of a moving outdoor target from a safe distance. To design this attack, SuperEar overcomes the challenges faced by traditional acoustic metamaterials, including low low-frequency gain and audio distortion during reconstruction. It successfully magnifies the speech signal by approximately 20 times, allowing the sound to be captured from the earpiece of the target phone. In addition, SuperEar optimizes the trade-off between the number and size of acoustic metamaterials, improving the portability and concealability of the interceptor while ensuring effective interception performance. This makes it highly suitable for outdoor tracking and eavesdropping scenarios. Through extensive experimentation, we have evaluated SuperEar and our results show that it can achieve an eavesdropping accuracy of over 80% within a range of 4.5 meters in the aforementioned scenario, thus validating its great potential in real-world applications.

Problem

• Outdoor Surveillance
• Long-Distance Eavesdropping
• Privacy Intrusion

Innovation

• SuperEar
• Acoustic Amplification
• Stealth Monitoring