BATGuard: Ultrasound-based Countermeasures Against Unauthorized Video Surveillance

This master’s thesis addresses the critical need to counter unauthorized video recordings in sensitive environments by developing and validating an experimental system for blocking illicit recordings in real-time. The proliferation of recording devices like smartphones and wearables, while technologically advanced, poses significant challenges to privacy, intellectual property, and physical security in settings such as research laboratories, government facilities, operating rooms, military zones, and strategic meetings. Traditional security measures are often insufficient due to the miniature size of modern cameras. This work proposes BATGuard: a solution using ultrasound to interfere with the internal stabilization mechanisms of consumer recording devices and, ultimately, to degrade their video recording capabilities. BATGuard adopts different ultrasound waves, precisely crafted to resonate with the gyroscopes and accelerometers embedded in camera stabilization circuits. This resonance induces artificial oscillations within the sensor system, causing the device to interpret motion even when it remains physically stationary. In response, the inertial stabilization system attempts to compensate for these non-existent movements, resulting in distorted and unstable video output. Initial experimentation employed both sinusoidal and random waveforms to broadly disrupt stabilization. Subsequently, efforts were directed toward refining control over the directionality of these injected phantom movements. This allowed for more targeted destabilization, manipulating the perceived motion along specific axes and enhancing the disruptive effect. The development process centered on practical experimentation with diverse hardware components to optimize their effectiveness, complemented by the implementation of custom software for precise ultrasound waveform control. The resulting system is designed for portability and adaptable deployment across various environments. The proposed solution was experimentally validated through simulated environments designed to understand its advantages, limitations, and potential applicability in more complex real-world scenarios. Evaluation metrics included the overall effectiveness of the countermeasure and the occurrence of false positives. The thesis, in its broader structure, will cover the theoretical background, a thorough state-of-the-art analysis, the system’s design and implementation, its experimental validation, before concluding with final considerations and proposals for future work.