You can save QR code as a file and initialize as many devices with it as you want. And by devices I mean proper smart cards personally, not old phones, but wha

You can save QR code as a file and initialize as many devices with it as you want. And by devices I mean proper smart cards personally, not old phones, but whatever floats your boat. This https://developers.yubico.com/ykneo-oath/Releases https://developers.yubico.com/ykneo-oath/Releases installed on a java card (cheaper than a yubikey) is perfectly usable with Yubico Authenticator on a modern smartphone over contactless interface.