In MacOS, navigate to System Preferences > Security & Privacy.
Check the box that says Allow your Apple Watch to unlock your Mac. You'll be prompted to enter your computer's password.
You're done! Your Mac will now unlock automatically when you're close to it.
If you're having issues, be sure to check the following:
- Make sure your Mac has bluetooth and wifi turned on
- Make sure your Apple Watch has a passcode enabled
- Make sure your Mac and Apple Watch are both signed into iCloud using the same Apple ID
- Make sure your Mac isn't currentlyusing internet or screen sharing