Google Deprecates Unlock with NFC Option
So Google has decided to remove NFC from it's "trusted devices" options for "Smartlock"
Google claims the lack of usage is to blame. People who had NFC paired for unlocking previous to September(ish, maybe June even) can still use theirs as long as they do not change it , or try to add new NFC pairings.
For the rest, new users, you can now only "trust" Bluetooth devices.
Clearly for us that doesn't work: bluetooth isn't precise enough to tell if a phone is in your hand or in the back seat of your car; must have it's own power; larger chips/antennas.
The Reddit thread contains links to Android/Google Bug Tracker threads, that maybe your voice can be added to, but who knows if Google will listen. Example:
If anyone finds a really great, trustworthy unlock app for Android, hit me up! Using an app with admin rights is far less secure than an OS inbuilt function. Derp Google.