TOTP (using Authy, Google Authenticator, or other apps) with a printed set of emergency recovery keys. And please, people, stop saying that this is not good fo

TOTP (using Authy, Google Authenticator, or other apps) with a printed set of emergency recovery keys. And please, people, stop saying that this is not good for people who do not have smartphones. To a first approximation, everybody has a smartphone.