I was playing around with the Mi Fit app and noticed an option to "Unlock device using band". Not needing an unlock pattern or PIN while you have a particular Bluetooth device nearby is pretty convenient. This however required allowing "Trusted devices" (Smart Lock) under the Security section in Settings but this was nowhere to be found.

Not sure if this is placed elsewhere for different variations of Android on say Samsung or Xiaomi devices, for Cyanogen OS 12 - Smart Lock needs to be turned on in "Lock screen" under Settings by selecting "Trust agents" as seen below.

Then you simply just make sure you toggle on "Smart Lock (Google)" and go through the introductory prompts. From there on, the "Smart Lock" section should now be available and you can set trusted devices among various other options.