In 2018, the U.S. Air Force applied for a patent that explains how wideband radar can be used to identify people by their bone structure.

A transmitting antenna sends a signal to a human, and that person’s biometric radar signature is compared against known signatures in a database.

For people with screws and metal bars in their bodies, this gives others a new way to identify you in a crowd: Your metal may be invisible to everyday people but turn into clear beacons when scanned.

Since 2018, a number of research papers have been published about the technology. In addition, scientists at the University of Arizona’s Department of Electrical and Computer Engineering have developed a way of measuring skeletal posture using mmWave radar and convolutional neural networks.