If you’re running version 18.104.22.168 of the MIUI 9 Global Stable ROM on the Xiaomi Redmi 4X, then you have likely noticed that it doesn’t have the Face Unlock feature available. This is a feature we recently saw announced with the launch of the Redmi Note 5 Pro (and many other Android devices as of late). However, thanks to XDA Junior Member shubhandu (and Exetron on 4pda.ru) we are now able to enable this feature on the Redmi 4X thanks to a flashable ZIP file in TWRP. So far, it has been tested and shown to be working on the Redmi 4/4X running this version of MIUI 9 and shubhandu has ported it to the Redmi Note 4 as well.
Check out this guide in our Redmi 4X forum