I got it to work! I don't have time to write it up fully, but if you can get an NFC Ring added as a trusted device under Smart Lock, the steps to use it seem to be:
- Wake up the phone - if Smart Lock is configured, there should be a closed, filled-in lock icon at the bottom of Android's lock screen with a pulsing circle around it.
- Scan the ring - if it recognizes it, the lock will open and change to an outlined image instead of filled, and a soft pop or click will play.
- Swipe away the lock screen, and the phone should be unlocked. The NFC Ring Unlock screen didn't appear, and I have access to my phone at that point.
I have my phone configured with a PIN, but can skip it and the still-active NFC Ring Unlock by scanning my ring. I can answer questions tomorrow, I'll try to check back.