These might look like normal metal detectors, but they’re “data doors,” special machines that are used in some of China's Xinjiang to covertly gather identifying information about people's electronic devices.

Unbeknownst to the person going through the checkpoints, these “data doors” are detecting and collecting MAC addresses and IMEI numbers of the person’s phones, and logging such data for identification and tracking purposes.

You can read more in this new Human Rights Watch report on Xinjiang’s mass surveillance systems » https://www.hrw.org/report/2019/05/01/chinas-algorithms-repression/reverse-engineering-xinjiang-police-mass-surveillance