Unlock your Mac and approve tasks with Apple Watch
When youโre wearing your Apple Watch, you can use it to automatically unlock your iMac and approve authentication tasksโsuch as entering passwords, unlocking notes and preferences, and authorizing installationsโwithout having to type a password. These features use strong encryption to provide secure communication between your Apple Watch and iMac.
To use the Auto Unlock and Approve with Apple Watch features:
Sign in with the same Apple ID on your Mac and Apple Watch.
Make sure your Apple Watch is unlocked and running watchOS 3 or later to automatically unlock your Mac; approving authentication requests requires watchOS 6 or later.
Turn on two-factor authentication (see below).
Set up two-factor authentication for your Apple ID. To turn on two-factor authentication, go to Apple menu 
> System Preferences > Apple ID > Password & Security, then select Set Up Two-Factor Authentication.
Make sure โDisable automatic loginโ is also selected. (You wonโt see this option if youโre using FileVault, but you can still use the Auto Unlock and Approve with Apple Watch features. For information about FileVault, see Encrypt Mac data with FileVault in the macOS User Guide.)
Set up Auto Unlock. Sign in with the same Apple ID on all your devices, then open System Preferences. If your Apple Watch has watchOS 6 installed, click Security & Privacy, then click General and select โUse your Apple Watch to unlock apps and your Mac.โ If your Apple Watch has watchOS 3 to watchOS 5 installed, select โAllow your Apple Watch to unlock your Mac.โ You canโt approve authentication tasks unless you have watchOS 6 or later.
Note: These features work only when your Apple Watch is authenticated with a passcode. You authenticate your Apple Watch each time you put it on, so no extra steps are necessary after you enter your passcode.
Skip the sign-in. Walk up to your sleeping iMac wearing your authenticated Apple Watch on your wrist, and press a key to wake your Mac. Apple Watch unlocks your Mac so you can get right to work.
Approve with Apple Watch. If youโre prompted for a password, double-click the side button on your Apple Watch to authenticate your password on your Mac. You can view your passwords in Safari, approve app installations, unlock a locked note, and more (requires watchOS 6).
Learn more. See Unlock your Mac and approve requests with Apple Watch in the macOS User Guide.