iPhone, iPad and Mac
The key lives in the keychain, bound to the biometrics enrolled when it was saved. Enroll another face or finger, and Vautir goes back to your master password.
Face ID, Touch ID, Android biometrics and Windows Hello open your vault without your master password, with a key your device's secure hardware gives up only to you.

Under Account, on each device, while Vautir is unlocked. It's that device's choice, and nothing about it reaches our servers.
A random key wraps this device's copy of your root key, and goes into the device's secure hardware.
The hardware hands the key back only after your face or finger. No password is typed.
The key lives in the keychain, bound to the biometrics enrolled when it was saved. Enroll another face or finger, and Vautir goes back to your master password.
The key is sealed by the Android Keystore, in StrongBox where the phone has one, and works only after a strong biometric check for that one unlock.
Windows Hello's own key stays in the computer's TPM, and the key that opens the vault is made from its signature each time, so it's kept nowhere.
The system keyring unlocks without the master password. It isn't biometric: turn it on only for a computer that locks with your own password.
Availability
Yes: to log in on a new device, and whenever biometrics change or fail. Keep it, and your Emergency Kit.
AutoFill opens the vault for one request and never asks for the master password: a password typed into a sheet over another app is one more place to be tricked out of it. So it needs biometrics turned on.
Free forever for unlimited passwords and devices. No card needed.