Researchers from the Karlsruhe Institute of Technology in Germany have confirmed that ordinary Wi-Fi signals can achieve near-perfect identification of individuals without the users carrying any electronic devices. This technology utilizes unencrypted beamforming feedback information exchanged between Wi-Fi devices and routers. By using machine learning to analyze changes in the signals caused by reflection and disturbance from the human body, it constructs human motion characteristics, achieving an identification accuracy rate close to 100% within seconds. The researchers warn that this discovery turns every router into a potential surveillance tool and call for enhanced privacy protection in new Wi-Fi standards.