"Google Authenticator" is the name of Google's TOTP app, which has become synonymous with the authentication method itself.</p> U2F and YubiKey OTP security keys <p>We have tested with a variety of different security keys, and any key that supports U2F should work. We do recommend YubiKey, as in our experience these have the best build quality, a slim profile, and are reliable. You can buy one from the Yubico store or via Amazon.</p> OTP devices <p>Many manufacturers are now selling standalone OTP devices, often in a credit card or key fob form-factor.