Science and Technology Daily, Beijing, October 16 (Reporter Zhang Mengran) – A new study reveals a worrying new type of surveillance danger: even without using Wi-Fi or turning off your phone, attackers could still identify people through the wireless networks around you. A team from the KASTEL Institute for Information Security and Reliability at the Karlsruhe Institute of Technology in Germany warns that attackers can use existing Wi-Fi signals in the environment to passively listen to changes in the propagation of radio waves and accurately infer the identity of people present, without any special hardware. The research paper was published in the latest issue of the journal *ACM Data Science*.

Team members explained that by observing how Wi-Fi radio waves are reflected and disturbed by the human body, they can "see" the surrounding environment and the people within it, much like a camera imaging. Therefore, it doesn't matter whether people are carrying or have Wi-Fi devices turned on. Even if the device is off or in airplane mode, as long as they are in a space with Wi-Fi signals, they can become a target for identification.

The key to this technology lies in the fact that devices in modern Wi-Fi networks periodically send signals called beamforming feedback to routers. These signals are originally intended to optimize network connection quality, ensuring that signals are transmitted more accurately to user devices. However, this feedback data is unencrypted during transmission, making it vulnerable to interception by anyone within signal range, including malicious eavesdroppers. By analyzing how these signals subtly change due to human movement and posture, and combining this with machine learning models, it is possible to construct human motion characteristics and thus identify specific individuals.

This means that every Wi-Fi router could potentially become an "observer." For example, when people pass by a café that provides Wi-Fi every day, even if they never connect to its network, their walking posture and body characteristics could still be recorded and used for subsequent identification. This surveillance could be exploited by cybercriminals for long-term tracking.

Unlike past surveillance technologies that relied on lidar or specialized sensors, this new method does not require expensive or easily observable equipment. Attackers only need a regular Wi-Fi receiver to eavesdrop on existing legitimate communications in the environment. Moreover, the danger lies in its "stealth," making it not only difficult to detect but also unrestricted by physical line of sight.

在一项涉及197名参与者的实验中，团队仅通过几秒钟的信号分析，身份识别准确率就接近100%，且不受观察角度或个人行走方式的影响。这一高精度识别能力，一方面凸显了强大的技术潜力，另一方面揭示了其中严重的隐私风险。