Two independent research teams have demonstrated that standard fiber optic internet cables can be converted into passive listening devices capable of capturing human speech, with the attack leaving no signature detectable by conventional counter-surveillance equipment.

Jack Lee Smith, a geophysicist at the University of Edinburgh, presented the findings May 8 at the European Geosciences Union (EGU) general assembly in Vienna, where his team demonstrated that distributed acoustic sensing (DAS), a technique originally developed to detect earthquakes by measuring changes in light reflections inside fiber cable, can recover intelligible speech from coiled cables within five meters of a speaker. Freely available AI transcription software produced accurate, real-time transcripts.

“Not many people realize that [fiber optic cables] can detect acoustic waves,” Smith said. “We show that in almost every case where you use these fibers, this could be a privacy concern.”

A team from the Hong Kong Polytechnic University and the Chinese University of Hong Kong presented a more operationally developed attack at NDSS Symposium 2026 in February. Their device wraps telecom fiber around a 65-millimeter cylinder to amplify nearby sound, can be disguised as ordinary networking hardware, draws no power at the listening location, and produces no radio emissions, rendering it undetectable by standard bug-sweeping equipment and ultrasonic jammers.

‼️🚨 NEW RESEARCH: Fiber-optic cables can be turned into a hidden microphone and used for eavesdropping.

Researchers from Hong Kong’s PolyU and CUHK just proved it works in real conditions. The paper was presented at NDSS 2026, one of the top cybersecurity conferences in the… pic.twitter.com/1x1Jt0YFMO

— International Cyber Digest (@IntCyberDigest) May 3, 2026

Most office and residential buildings contain multiple dormant fiber strands from different internet service providers, the researchers noted. “Usually, only one fiber is in active use, while the others remain unused,” the paper stated, identifying these strands as potential eavesdropping channels for anyone with physical access to network infrastructure.

Frederik Tilmann, a seismologist at GFZ Helmholtz Centre for Geosciences, noted that DAS applied to deep-sea cables can also detect submarine and ship movements. The findings carry “military and security implications that need to be considered before sharing data openly,” Tilmann said.