[greatjack613]

I am more curious about the technical aspect.

I could not find any android documentation on building wifi nfc tags that are automatically connected to by the system.

Can someone explain how this is working? Hidden apis? A NFC spec, or something else?

[parliament32]

https://developer.android.com/reference/android/provider/Set...

https://source.android.com/devices/tech/connect/wifi-easy-co...

[wccrawford]

https://www.digitaltrends.com/how-to/diy-nfc-coasters/ This has some steps to use your phone to create the NFC Sticker.