How can I use an NFC tag to unlock my device It seems that some of the NFC lock apps don't integrate into the native lock-screen, but present a custom home screen that blocks access to native home screen.  

This appears to result a range of issues for the various app solutions, or the apps never get out of beta.

How can I keep the native lock screen and enable NFC unlock?
This can be done since Lollipop with the help of Play Services.


Go Settings > Security > Trust Agents
Enable Smart Lock (Google)
Go Settings > Security > Smart Lock > Trusted Device > Add trusted device > NFC


https://support.google.com/nexus/answer/6093922?hl=en-GB