It's just a simple nfc tag, but manufactured in a bio-compatible form like a pet tag. 

You can write whatever data you want to them, be it access control credentials, vCards, urls, text...

In this case I was using LNurlW to create a LN faucet so people could receive sats just by tapping their phone to my hand. 

 Yes, I know. But how did you put it in? That's what I want to know.