Your Router Can Detect Breathing Through Walls. Is That a Search?
The Technology Is Real, Standardized, and Already in Your House
This is the part of the conversation where people expect a lawyer to say the fear is overblown. It is not overblown. Wi-Fi sensing is a published industry standard, it is built into current router chipsets, and it detects human movement through walls without a camera. What is genuinely uncertain is not the technology. It is whether the Fourth Amendment reaches it. Ava asked attorney Michael Benavides to separate the engineering from the law.
Ava Asks, Michael Answers — Wi-Fi Sensing, Plain English
Ava: What is Wi-Fi sensing?
Michael, Esq.: Wi-Fi is radio. Radio waves reflect off bodies and objects and arrive at the receiver slightly distorted. Wi-Fi sensing reads those distortions — the technical term is Channel State Information — and reconstructs what caused them. Your router is already receiving this data. Sensing is the decision to interpret it rather than discard it.
Ava: What can it detect?
Michael, Esq.: Motion. Presence. How many people are in a space. Gestures. Whether someone has fallen. And respiration — the rise and fall of a chest. No camera and no microphone are involved.
Ava: Through walls?
Michael, Esq.: Wi-Fi passes through drywall, wood and glass. That is why it works in your house at all. The same physics means the sensing device does not need to be in the room, and in some configurations does not need to be in the building.
Ava: Is this experimental?
Michael, Esq.: No, and that is the part people have not caught up to. It became an official IEEE standard — 802.11bf — in September 2025. Standardization means it goes into chipsets, and chipsets go into ordinary consumer routers. In February 2026, ADT paid a reported $170 million for a Wi-Fi sensing company. This is a commercial product line, not a laboratory demonstration.
Ava: Can it tell who a person is?
Michael, Esq.: Research reported in 2026 out of the Karlsruhe Institute of Technology in Germany indicated that individuals could be identified with high accuracy by how they uniquely disturb the signal — essentially a gait signature. I would want to read the underlying paper before I characterized the accuracy figures in a filing, and anyone citing this should do the same. But the direction is clear: the question has moved from whether someone is present to which person is present.
Ava: Now the law. What governs this?
Michael, Esq.: The controlling case is Kyllo v. United States, decided in 2001. Agents pointed a thermal imager at a home from a public street to detect heat consistent with indoor marijuana cultivation. The Supreme Court held that was a search. Justice Scalia's rule was that where the government uses a device to explore details of the home that would previously have been unknowable without physical intrusion, that is a search — at least where the technology in question is not in general public use.
Ava: That sounds like it covers Wi-Fi sensing exactly.
Michael, Esq.: On the facts, it fits better than the thermal imager did. Kyllo was about heat blooms on an exterior wall. Wi-Fi sensing reports breathing and gait inside rooms. If anything it is a more intrusive intrusion into the home, and the home is the place the Fourth Amendment protects most strongly.
Ava: So where is the problem?
Michael, Esq.: In the qualifier. Kyllo's protection was expressly tied to technology not in general public use. In 2001 a thermal imager was exotic. Wi-Fi sensing is being standardized into consumer hardware and sold by a home security company. The more ordinary it becomes, the weaker that clause gets.
Ava: That seems backwards.
Michael, Esq.: It is the structural weakness in the doctrine, and it is worth stating plainly: a privacy rule keyed to obscurity expires when the technology succeeds. The more of these routers ship, the harder it becomes to argue that a homeowner reasonably expects the inside of their home to be unreadable. The protection erodes precisely as the capability spreads.
Ava: Is there a counterargument?
Michael, Esq.: Several, and I think they are strong. First, general public use should mean the public commonly uses the technology for that purpose — owning a router that could sense is not the same as the public routinely surveilling interiors. Second, Kyllo's deeper principle was about preserving the degree of privacy that existed when the Fourth Amendment was adopted, and that principle does not evaporate because a chipset got cheap. Third, and newest, the Supreme Court's June 2026 decision in Chatrie emphasized the character of the information rather than the mechanism — records a person reasonably regards as their own stay protected. Breathing inside your bedroom is about as squarely your own as information gets.
Ava: Has a court decided this?
Michael, Esq.: Not to my knowledge, and I want to be honest about that. I am not aware of controlling authority applying the Fourth Amendment to Wi-Fi sensing. This is an argument, not a holding. Anyone who tells you the law here is settled is telling you something that is not true yet.
Ava: What about a private party doing it — a landlord, an employer, an ex?
Michael, Esq.: Different framework entirely. The Fourth Amendment restrains the government, not your neighbor. Private conduct runs through other law — California's constitutional privacy right, intrusion upon seclusion, stalking and electronic harassment statutes, landlord-tenant law, and potentially the wiretap and eavesdropping provisions depending on what was captured. That is a fact-specific analysis and a different consultation.
Ava: And the disclosure problem?
Michael, Esq.: This is what bothers me most as a practical matter. Video surveillance carries social and legal expectations of visibility — you can see a camera. Wi-Fi sensing is invisible. Reporting indicates there is no standard notification, no simple way to disable it, and no legal requirement that manufacturers or providers disclose the capability exists. A person in a home currently has no reliable way to know whether their router is doing this. That is a legislative gap, and California has legislated in this space before.
What to Do
Wi-Fi sensing uses Channel State Information — the distortion of radio signals by bodies — to detect motion, presence, occupancy counts, gestures, falls and respiration without a camera or microphone, and it works through common building materials. It became IEEE standard 802.11bf in September 2025 and is present in current consumer router chipsets; in February 2026 ADT acquired a Wi-Fi sensing company for a reported $170 million, and 2026 research from the Karlsruhe Institute of Technology indicates individuals may be identifiable by their signal signature. The governing Fourth Amendment authority is Kyllo v. United States, 533 U.S. 27 (2001), which held that using a device to obtain details of a home's interior otherwise unknowable without physical intrusion is a search — but conditioned that on the technology not being in general public use. That qualifier is the vulnerability: as sensing becomes ordinary consumer equipment, the clause that protects homeowners weakens. Counterarguments exist — that general public use should mean common use for surveillance purposes, that Kyllo's core principle preserves founding-era privacy regardless of cost curves, and that Chatrie (2026) emphasizes the character of the information over the mechanism. No controlling authority has yet applied the Fourth Amendment to Wi-Fi sensing; this remains argument, not holding. Private-party sensing is governed by different law entirely. If you believe sensing technology has been used against you, a V2K and RF Defense consultation in Sacramento, Stockton, or Modesto can assess which framework applies.
Next and last in this series: what to actually do — and what evidence actually helps — if you believe you are being monitored inside your home.
V2K & RF Defense | Blue Data Law | Michael Benavides, Esq., CA Bar No. 270714 | Sacramento, Stockton & Modesto | 707-362-4166 | attorneymichaelbenavides.com
ATTORNEY ADVERTISING. V2K & RF Defense and Blue Data are content brands of the law practice of Michael Benavides, Esq., California State Bar No. 270714. Ava is an editorial brand voice, not an attorney; only Michael Benavides, Esq. provides legal analysis. General information only — not legal advice; no attorney-client relationship is formed by reading this. Authority referenced (Kyllo v. United States, 533 U.S. 27 (2001); Chatrie v. United States, 609 U.S. ___ (2026)) is as of July 2026. Technical claims regarding IEEE 802.11bf and Wi-Fi sensing capability are drawn from published industry and press reporting and academic research summaries; capabilities vary by hardware and configuration, and the referenced identification research should be evaluated against its primary source. No court has been identified as having applied the Fourth Amendment to Wi-Fi sensing; the analysis above is argument rather than settled law. Confirm current law and current technical facts before acting. This article describes general principles only and does not reference any actual client or pending matter. Prior results do not guarantee a similar outcome.


