At present, most offline fingerprint phones use optical solutions. In short, OLED screen emits light to illuminate the finger area, and the reflected light that illuminates the fingerprint returns to the sensor close to the screen through the gap of the screen pixels. The obtained fingerprint image is compared with the first input image of the mobile phone, and finally the recognition judgment is carried out.
The sensor here actually contains CMOS, which is a small camera.
Following this idea, some foreign Netizens found the activity launcher app, and easily opened the debugging mode of Xiaomi 9t with huiding fingerprint module, so a new front lens was unlocked.
Because the CMOS mainly collects fingerprint information, the pixel of the picture is low and almost has no usability. However, this still caused the vigilance of foreigners, saying that Xiaomi or huiding still lacks privacy protection. After all, a three-party app can easily open the debugging mode. If it is really used by criminals, it may not be the result you want to see.