Unlock with PIN
You can set a PIN code as a method for unlocking your vault. PINs can only be used to unlock your Vault, you will still be required to use your master password and any enabled two-step login method when you log in.
If you're not sure of the difference, scroll down to Understanding Unlock vs. Log In.
After 5 failed PIN attempts, the app will automatically log out of your account.
Enable Unlock with PIN
Unlock with PIN can be enabled for the Bitwarden browser extension, mobile app, and desktop app:
If you turn off the Lock with master password on restart option, the Bitwarden application may not fully purge sensitive data from application memory when entering a locked state. If you are concerned about your device's local memory being compromised, you should keep the Lock with master password on restart option turned on.
Understanding Unlock vs. Log In
In order to understand why unlocking and logging in aren't the same, it's important to remember that Bitwarden never stores unencrypted data on its servers. When your Vault is neither unlocked nor logged in, your Vault data only exists on the server in its encrypted form.
Logging in to Bitwarden decrypts your Vault data to your device. In practice, that means two things:
Logging in will always require your Master Password, because your Master Password is the source of the key needed to decrypt your Vault data. Additionally, because decryption is an operation that needs to be protected, this stage is where any enabled Two-step Login methods would be required.
Logging in will always require you to be connected to the internet (or, if you're self-hosting, connected to the server), because you need access to the encrypted Vault in order to decrypt it.
Unlocking can only be done when you're already logged in. In other words, only when your Vault data is already stored (encrypted) on your device. Because your Vault is already downloaded and your decryption key stored in memory:
You don't need to be connected to the internet (or, if you're self-hosting, connected to the server).