Zen
Set up two-factor sign-in
Two-factor sign-in is on. These backup codes each work once, if you lose your phone. Keep them somewhere safe, away from this computer.
Security
Signed-in browsers
Device keys
For things that cannot type a code: the Apple Watch app, Siri Shortcuts, scripts. A key is shown once; revoke it here if a device is lost.
Copy this key now; it will not be shown again.