Apple Watch unlocking Mac not working?

If you're an Apple Watch owner and a Mac user, there's a nifty feature that allows your Apple Watch to unlock your Mac automatically. This makes it convenient especially if you're in an office setting and you're constantly in and out of your desk.

To enable this feature, just go to "System Preferences" and then "Security & Privacy". There, you should be able to see under the General tab the option "Allow Your Apple Watch to unlock your Mac". Check it, and you should be done.

To lock your machine when you're leaving your desk, just press and hold down "control" + "shift" and the "power" button. When you're back, make sure you're wearing your watch and it's unlocked, just tap on the mouse pad or any key on the keyboard and your Mac should automatically unlock.

If you're using a company issued Mac, they may put in place security policies that requires you to change your password every so often. Note that once the Mac password is changed, it will mess up this Apple Watch unlock feature causing the Auto Unlock with Apple Watch to stop working. To fix this, you need to head over to "Keychain Access" (Just hit command + space bar to bring up Spotlight and type in "Keychain Access"). Then follow these steps:

1. Click “login in” the Keychains list.
2. Choose Edit > Change Password for Keychain “login.”
3. If the keychain is locked, enter the previous user password for the computer, then click OK.
   If you entered the correct password, a new window appears.
4. Enter the previous user password again in the Current Password field.
5. Enter your new user password in the New Password field.
6. Reenter the new user password in the Verify field, then click OK.  

You can learn more about it here: https://support.apple.com/en-sg/guide/keychain-access/if-you-need-to-update-your-keychain-password-kyca2429/mac

Every so often, you may encounter that the Change Password for Keychain "login" greyed out. If this happens, you may have to manually fix this using Terminal. To access terminal, use Spotlight Search (command + space bar) and type "terminal". Terminal.app will appear. Select that.
Then in the terminal prompt and type in "security set-keychain-password" (Without the ""). It will then prompt for Old Password and then the New Password twice. Key those in accordingly. Then head back to System Preferences > Security & Privacy, and enable the Apple Watch unlock option again.

Hope this helps.