It’s easy to find NFC or RFID rings these days. Adafruit sells them, but the electronics shop knows that it caters mainly to makers, so it came up with a guide for a customizable 3D printed ring.
The ring gets is power from Adafruit’s micro NFC transponder. The shop is also sharing its ring 3D model, which you can edit to your taste and size.
Tap this link to read Adafruit’s full guide.