Hackers Can Hear Through Walls Using Radio Waves

Your laptop’s microphone is broadcasting everything it hears as radio waves that can pass through concrete walls and be captured by anyone with basic equipment costing under $100.

Security researchers have discovered that modern digital microphones in laptops and smart speakers unintentionally leak audio as electromagnetic signals, creating a new form of wireless eavesdropping that requires no hacking, no malware, and no physical access to your device. The vulnerability affects millions of devices worldwide and could expose private conversations to corporate spies or government surveillance.

The attack works because of how digital microphones process sound. These tiny components, called MEMS microphones, convert audio into digital pulses that contain remnants of the original speech. Those pulses create weak radio emissions that leak out of devices like invisible broadcasts.

“With an FM radio receiver and a copper antenna, you can eavesdrop on these microphones. That’s how easy this can be,” said Sara Rampazzi, a professor of computer and information science and engineering at the University of Florida who co-authored the new study. “It costs maybe a hundred dollars, or even less.”

Ghost Voices Through Concrete

The researchers proved their point using eerie demonstrations. A woman’s voice, distorted by static but clearly understandable, emerged from radio equipment as she spoke test sentences like “The birch canoe slid on the smooth planks” and “Glue the sheet to the dark blue background.” Each transmission passed through concrete walls up to 10 inches thick.

The team tested laptops, Google Home smart speakers, and video conferencing headsets. Laptops proved most vulnerable because their microphones connect through long internal wires that act like antennas, amplifying the leaked signals.

What makes this attack particularly concerning? Your microphone doesn’t need to be actively recording. Simply having common applications open—Spotify, YouTube, Amazon Music, or Google Drive—can enable the microphone enough to leak radio signals of nearby conversations.

AI Makes It Worse

The researchers didn’t stop at proving they could capture garbled audio. They fed the radio-intercepted recordings into commercial speech-to-text software from companies like OpenAI and Microsoft. The AI systems successfully cleaned up the static and converted the eavesdropped conversations into searchable text.

In controlled tests, the attack achieved 94.2% accuracy in recognizing spoken digits from up to two meters away, even when the target laptop sat behind a 25-centimeter concrete wall. For longer sentences, the system maintained a transcription error rate of just 14%—good enough to understand most conversations.

The implications stretch far beyond privacy concerns. Industrial espionage becomes possible without ever touching a competitor’s equipment. Government surveillance could operate invisibly, requiring only a van parked outside a building. Corporate meetings held in supposedly secure rooms could be monitored from the parking lot.

The Technical Breakthrough

What wasn’t highlighted in initial reports is the researchers’ discovery that multiple harmonics of the digital pulses retain acoustic information. This finding reveals why the attack works so effectively—it’s not just one frequency leaking audio, but several frequency bands that can be combined to reconstruct speech with surprising clarity.

The vulnerability stems from pulse-density modulation, the method these microphones use to convert analog sound waves into digital data. Each pulse contains traces of the original audio, and when thousands of these pulses transmit per second, they create a radio fingerprint of everything the microphone hears.

Key findings from the research include:

• Attack works through concrete walls up to 25 cm thick
• Simple copper tape antennas prove as effective as professional equipment
• No software installation or device tampering required
• Commercial AI dramatically improves transcription accuracy
• Multiple device types affected, with laptops most vulnerable

Solutions on the Horizon

The researchers identified several potential fixes. Moving microphones away from long cable runs inside laptops could reduce signal amplification. Tweaking audio processing protocols might scramble the leaked information beyond useful recovery.

A more sophisticated defense involves randomizing the timing of the digital pulses, making it nearly impossible for attackers to extract coherent audio from the radio emissions. Think of it as adding white noise directly to the electromagnetic signature.

The team has shared these defensive strategies with device manufacturers, though it remains unclear whether companies will implement the changes in future products. Until then, the invisible radio chatter from millions of microphones continues broadcasting our private moments to anyone listening on the right frequency.

For now, users have limited options beyond being aware that their devices might be transmitting more than they realize. The age of assuming our private conversations stay private may be ending, one radio wave at a time.