Internet Powered · 8 September 2026
You walk across the living room without touching a phone, switching on a light, or speaking. Could the Wi-Fi notice?
Yes. A system equipped for Wi-Fi sensing can detect movement by measuring how your body changes the radio signals traveling through a space. You do not need to carry a connected device. Your body becomes part of the environment the signal passes through. Researchers have demonstrated this kind of device-free sensing using ordinary Wi-Fi transmissions. [1]
The central idea is simple: when you move, the received signal changes. Sensing software looks for those changes. Turning that physical effect into useful information requires a sensing system; the presence of a Wi-Fi connection alone does not tell you what a particular product can detect.
A router sends radio signals to connected devices. Those signals do more than travel directly across the room. They also encounter walls, furniture and people. Some energy reflects; some is absorbed or passes through. NIST describes how even the movement of a breathing chest can alter the signal’s path. Walking across a room changes that environment more noticeably. [2]
At the receiver, signals arriving along different paths combine. As you move, those paths and their contributions change. The receiver can therefore encounter a changing pattern even though the devices themselves stay in place. Engineers call these multiple routes multipath. For sensing, their changes provide clues about movement in the surrounding space. [3]
That is why the idea of an invisible tripwire is only partly helpful. It suggests that a person must break one straight beam between two devices. Real indoor radio propagation involves reflected paths too. A sensing system may respond to movement affecting those paths, beyond that imaginary straight line. The room itself helps shape what can be measured. [4]
To extract useful information, many systems use channel state information, or CSI: detailed measurements of how the wireless channel affects a signal. These include amplitude—how strong its components are—and phase, their position within a wave cycle. CSI offers much more detail than a simple signal-strength reading or the Wi-Fi bars on your phone. [4]
Software examines measurements over time and decides whether the changes indicate motion. Signal processing, thresholds or machine-learning models can turn those changes into an event. The useful output might be as simple as “motion detected.” It is an interpretation of radio measurements, not a photograph produced by the receiver. [3]
The equipment and software matter. Espressif’s public development project includes examples for collecting CSI with compatible chips, including a receiver working with a router, and software for human-activity detection. This shows how existing radio hardware can support an additional task when the necessary measurements and processing are available. It does not make every Wi-Fi device a finished motion sensor. [5]
There is also a published standard for this field: IEEE 802.11bf-2025, released in September 2025, adds enhancements for wireless LAN sensing. Its existence establishes a standardized technical framework; it does not mean every installed router implements it or that every sensing product offers the same capabilities. [6]
Consumer versions already exist. Xfinity describes WiFi Motion as an opt-in feature using compatible gateways and stationary connected devices. The company says it detects movement without cameras, does not identify specific people, and does not track movement’s exact location. That is a useful example of the difference between sensing an event and understanding everything happening in a room. [7]
A further distinction matters: motion and presence are different questions. Someone can be present while sitting nearly still. Detecting that person may require sensitivity to much smaller movements. NIST and FDA researchers demonstrated detection and classification of simulated breathing patterns using a breathing manikin, commercial Wi-Fi equipment and modified router firmware. That controlled experiment supports the possibility of fine movement sensing; it does not establish that an ordinary home motion feature can monitor someone’s breathing or health. [2]
Coverage also depends on the setting. Xfinity warns that device placement, home layout and building materials can affect detection. Consequently, good internet coverage should not be treated as proof of reliable motion coverage. A system needs to be evaluated where it will actually operate, for the movement someone expects it to detect. [7]
Can it work through walls? Sometimes. University of Chicago and University of California, Santa Barbara researchers demonstrated an outside receiver detecting indoor motion by listening to existing Wi-Fi signals, without breaking network encryption. This is a demonstrated capability under tested conditions, not evidence that any nearby person can reliably monitor any home. [8]
Camera-free sensing can still create personal information. Xfinity says its motion-event history is stored in its cloud systems for seven days. Even a record of when movement occurred can suggest household routines—an implication of keeping activity history, rather than proof that a service identifies particular people. [7]
Wi-Fi can therefore do two jobs with the same underlying radio technology: carry information between devices and supply clues about movement around them. The body changes the signal. The sensing system turns that change into a useful observation. Understanding that relationship explains both why Wi-Fi motion detection works and why its limits depend on the system interpreting it.
Source Library
Sources checked 7 September 2026.
[1] Et Tu Alexa? When Commodity WiFi Devices Turn into Adversarial Motion Sensors
Yanzi Zhu, Zhujun Xiao, Yuxin Chen, Zhijing Li, Max Liu, Ben Y. Zhao, and Haitao Zheng. NDSS 2020; linked revision 11 January 2020.
URL: https://arxiv.org/html/1810.10109v4
[2] Wi-Fi Could Help Identify When You’re Struggling to Breathe
National Institute of Standards and Technology (NIST). 20 December 2022; updated 3 February 2025.
URL: https://www.nist.gov/news-events/news/2022/12/wi-fi-could-help-identify-when-youre-struggling-breathe
Synaptics. Publication date not stated.
URL: https://www.synaptics.com/technology/wireless-technology/wi-fi-sensing
[4] Introduction to ESP-CSI Solution
Espressif Systems. Publication date not stated; living documentation.
URL: https://docs.espressif.com/projects/esp-techpedia/en/latest/esp-friends/solution-introduction/esp-csi/esp-csi-solution.html
[5] ESP-CSI: Applications based on Wi-Fi CSI
Espressif Systems. Publication date not stated; maintained repository.
URL: https://github.com/espressif/esp-csi
[6] IEEE 802.11bf-2025 — Enhancements for Wireless LAN Sensing
IEEE Standards Association. 26 September 2025.
URL: https://standards.ieee.org/ieee/802.11bf/11574/
[7] Detect Movement in Your Home with WiFi Motion
Xfinity / Comcast. Publication date not stated.
URL: https://www.xfinity.com/hub/smart-home/wifi-motion
[8] How hackers could use Wi-Fi to track you inside your home
Rob Mitchum / University of Chicago. 14 November 2019.
URL: https://news.uchicago.edu/story/how-hackers-could-use-wi-fi-track-you-inside-your-home
