Scientists: Wi‑Fi Can Image and Track People — Even When Devices Are Offline

Researchers warn a rising surveillance technique can turn ordinary Wi‑Fi radio traffic into images and motion traces of people — without their knowledge or consent.

How This Works

Modern Wi‑Fi uses beamforming to improve performance. Devices connected to a Wi‑Fi network send beamforming feedback information (BFI) so transmitters can shape radio beams. That feedback is often transmitted unencrypted. When radio waves bounce off a person, the reflected patterns change the expected signals; captured BFI reveals those changes. By analyzing many such reflections, an adversary can reconstruct radio‑based snapshots of people, infer motion, and even identify individuals across different gaits and viewpoints.

Why It’s A Privacy Threat

Unlike web trackers that rely on browsing data, BFI‑based sensing requires no access to your phone, apps, or browsing history and needs no specialized sensors. An attacker only needs to record the BFI broadcast over the air to capture human presence and movement within a Wi‑Fi network’s range. This makes the technique especially concerning in public spaces, workplaces and homes where Wi‑Fi is ubiquitous.

What The Research Shows

The study by Julian Todt, Felix Morsbach and Thorsten Strufe of KASTEL Security Research Labs (Karlsruhe Institute of Technology) — presented at the 2025 ACM SIGSAC Conference on Computer and Communications Security — demonstrates that BFI can be used to identify people with high accuracy across different walking styles, viewpoints and large sample sets.

“With Wi‑Fi networks being ubiquitous in our everyday lives, the impact of unknown privacy threats is likely severe,” the researchers wrote.

Standards, Risks, And Open Questions

Earlier channel‑state information (CSI) was limited to specific hardware and applications, which reduced misuse. Wi‑Fi 5 introduced widespread beamforming support and unintentionally made BFI‑based sensing easier. The IEEE is now moving to standardize sensing capabilities for Wi‑Fi, which could expand these capabilities further unless privacy protections are incorporated.

Key open questions include how individual features and mannerisms shape beamforming reports, how robust identifications are in diverse real‑world settings, and which practical countermeasures will be effective at scale.

Possible Mitigations

Some potential defenses exist but are incomplete: encrypting beamforming feedback, limiting or randomizing feedback reports, applying firmware updates that restrict access to raw BFI/CSI, and designing standards that include privacy safeguards. Network operators and device manufacturers will need to weigh performance tradeoffs against privacy risks and invest in testing mitigations in the wild.

Why This Matters

Because BFI can be recorded without special hardware or custom firmware, the barrier to misuse is low. If left unaddressed, techniques that convert routine Wi‑Fi transmissions into sensing tools could be used by malicious individuals, companies, or state actors to monitor movement and behavior wherever Wi‑Fi is present.

As the researchers caution, we should not assume connectivity improvements come without cost — and standards bodies, vendors and security researchers must act now to close these privacy gaps.

Maybe it’s time to rewrite the chorus of Rockwell’s “Somebody’s Watching Me” to include a verse about Wi‑Fi.