Overview

• Modern pulse-density modulation microphones unintentionally emit radio-frequency signals that carry audio data whenever they process sound
• Researchers demonstrated that a basic setup with copper-foil antennas and standard receivers can intercept conversations through walls and up to two meters away with over 94% accuracy
• Major microphone suppliers including Knowles, STMicroelectronics and TDK-InvenSense all showed the same design flaw in independent tests
• Experiments revealed that microphones often remain active during audio playback or when apps appear muted, enabling continuous, covert surveillance
• A hardware-level countermeasure using spread-spectrum clocking cut interception success from more than 70% to under 5%, prompting calls for device redesigns