Big Sur - Unlocking with Apple Watch

I had the same issue with Apple Watch 6 (watchOS 7.1) and MacBook Pro 13 early 2015 (Big Sur). So I repaired it with some steps:

1) I disabled Keychain synchronisation on MacBook (Settings/iCloud/Keychain)

2) I made steps in this thread https://discussions.apple.com/thread/251803595?answerId=253458029022#253458029022

• • Open "Keychain Access"
  • In "View", enable "Show Invisible Items"
  • Search for "Auto Unlock"
  • You should see a whole bunch of application passwords for "Auto Unlock: XXXX's ..."
  • Select all records and delete (this will reset/disable auto unlock on other Macs if you use multiple Macs)
  • Whilst still in "Keychain Access", search for "AutoUnlock" (no space)
  • There should be 4 entries for "tlk" "tlk-nonsync" "classA" "classC"
  • Select 4 records and delete (don't worry if they re-appear, the system repairs this automatically)
  • Open "Finder" and navigate to "~/Library/Sharing/AutoUnlock"
  • There should be two files "ltk.plist" and "pairing-records.plist"
  • Delete both files

3) Disconnected Watch from iPhone

4) Connected back Watch to iPhone (set it from backup)

5) Restarted MacBook

6) Turned on Keychain in iCloud settings

7) Enabled Auto Unlock for Watch in System Prefs

This was the first thread that popped up when I googled the question, so I'm just gonna paste the response by @Stoska992 from this thread;

I've finally fixed it! I found a bunch of errors related to "AutoUnlock" in the Console that was hinting to me that there was some invalid state on my Mac with keys and plists not being reset properly. 

Steps (follow at your own discretion)

1. Open "Keychain Access"
2. In "View", enable "Show Invisible Items"
3. Search for "Auto Unlock"
4. You should see a whole bunch of application passwords for "Auto Unlock: XXXX's ..."
5. Select all records and delete (this will reset/disable auto unlock on other Macs if you use multiple Macs)
6. Whilst still in "Keychain Access", search for "AutoUnlock" (no space)
7. There should be 4 entries for "tlk" "tlk-nonsync" "classA" "classC"
8. Select 4 records and delete (don't worry if they re-appear, the system repairs this automatically)
9. Open "Finder" and navigate to "~/Library/Sharing/AutoUnlock"
10. There should be two files "ltk.plist" and "pairing-records.plist"
11. Delete both files
12. Open "System Preferences" and try enabling auto unlock. You may need to enable it twice, the first attempt will fail.

Update to watchOS 7.1, as it has a fix for unlocking Macs

If that does not work, it should, but if it does not work, then read the following threads

Check out this thread on fixing Apple Watch unlocking Mac

https://discussions.apple.com/thread/251803595?answerId=253458029022#253458029022

Then follow with this thread

https://discussions.apple.com/thread/251826134?answerId=253504359022#253504359022

And

I also found that it took awhile for the iCloud Keychain records to propagate and merge on all the systems. More so when you have multiple devices sharing the keychain (I have 4 Macs, the iPhone, and the Apple Watch). I followed both of the above threads, but it was not reliably working until the next day, when I tried again. And I did have to click the enable check box twice the next day, but then it stuck.

And this thread says they also had to toggle the Apple Watch -> Settings -> Siri -> Listen for "Hey Siri" option off then on

https://discussions.apple.com/thread/251803595?answerId=253782332022#253782332022

Hints (you will understand when you read the first and second threads):

Applications -> Utilities -> Keychain Access

Finder -> Go menu -> ~/Library/Sharing/AutoUnlock

System Preferences -> iCloud -> Keychain

I have a Series 4 with watchOS 7.1 and MBP 13 2018 (BigSur 11.0.1). These steps worked for me. A few minor details/differences:

1. I was unable to access the ~/Library/Shared folder to delete the plist files. Tried via Finder or attempting to sudo in. I skipped this step and everything seemed to come out OK.
2. Took me a minute to understand what was meant in step 3 - Disconnected Watch from iPhone. I believe you meant go into the iWatch app on your phone. Select General->Reset->Erase Apple Watch Content and Settings. Which is what I did. This basically resets it to factory.
3. Pair your Watch with your phone again. The process is like it was out of the box new, but you'll have a restore from backup option. Which I also did. Make sure your battery levels are up. Takes 15-20 mins to restore from backup.
4. When you turn on keychain sync again the checkbox will be grey. Wait until it turns blue to confirm sync.
5. If you use a VPN, disable it before trying to turn on Auto Unlock for Watch under System Pref->Security&Privacy->General. I kept getting errors that my Mac couldn't communicate with my watch until I turned off VPN. Worked immediately once VPN was off.
6. Once paired I turned on my VPN and it looks like everything is good to go and I can unlock successfully now.

I've had intermittent success with watch unlock for over a year now. It started working reliably with the watch 7.1 update and then Big Sur promptly broke it again. Fingers crossed things are stable from here!

+1 on this.  With bartlomiej's instructions on 11.0, watch unlock has worked reliably for the first time in over a year. I update to 11.1. Stops working again!  Infuriating! This is one of the most useful features of iWatch if you own a Mac!  

Dear Apple, I get it's complicated due to all the security hoops and Bluetooth flakiness, but c'mon! You're GD Apple! Your trademark is making complicated things easy! Don't put the feature in, if you can't make it work!

The real irony? The release notes for 11.1 lists a bug fix saying, "Unlocking Mac automatically with Apple Watch problems."

I tried the reset instructions from bartlomiej again with a couple of small tweaks (no VPN, disable unlock with watch, and skipped deleting files). Here's the modified steps (with a few less details on cert names etc).

1. VPN off. This may not be necessary, but I know there are a lot of networky things going on under the covers so I turned mine off just in case.
2. Disabled unlock with my watch in sys security preferences
3. Disable iCloud keychain sync in prefs
4. Open keychain access app
5. In the menu: view->show invisible items
6. Search for Auto Unlock (space)
7. Selected all records and deleted them. I had a really old extra one in there over what bartomiej listed. Still deleted them all.
8. Search for AutoUnlock (no space)
9. Delete all those records
10. Went into watch app on my phone and reset my watch back to factory
11. Re-paired and restored my watch from backup with the iWatch app on my phone
12. Rebooted my Mac. Did this while I waited for my watch to restore.
13. Once my watch was restored, I turned key chain sync on in iCloud sys prefs
14. Then turned on "unlock with my watch" in sys security prefs.

Notes:

When I tried to restore my watch from a backup I got obscure errors with "nul" references for both of my backups.  I reset pairing on my watch app and tried a second time. Got the latest backup to restore after another 10 minutes of waiting.

I had a couple of failures that my Mac couldn't communicate with my watch when trying to enable watch unlock in sys prefs. After a few retries it enabled and I tried logging in.  An "unlocking with watch" message showed up and then it failed. Repeat login attempt a few times.  Still failed. 

Waited a few minutes (maybe 5?). Tried again, and it seems to be working now. I'm guessing the watch was overloaded synch'ing up with my phone data and my Mac couldn't get a word in during these steps.

I don't know if it's possible to have a more un-Apple experience than this.

For me the helpful comment didn't solve the issue.

Instead, what did solve the issue for me was:

1. Sign out from iCloud on your Mac
2. Restart Mac
3. Sign in to iCloud
4. Enable unlock with watch.

This solved the issue for me.

Only had to do these steps and then checked the box to turn on the settings and it works!! Hooray. I haven’t been able to unlock my Mac with my watch since upgrading to the 16inch MacBook 6 months ago!!!

• Open "Keychain Access"
• In "View", enable "Show Invisible Items"
• Search for "Auto Unlock"
• You should see a whole bunch of application passwords for "Auto Unlock: XXXX's ..."
• Select all records and delete (this will reset/disable auto unlock on other Macs if you use multiple Macs)
• Whilst still in "Keychain Access", search for "AutoUnlock" (no space)
• There should be 4 entries for "tlk" "tlk-nonsync" "classA" "classC"
• Select 4 records and delete (don't worry if they re-appear, the system repairs this automatically)

After installing Big Sur 11.2 update today, I can finally check the 'Use your Apple Watch to unlock apps and your Mac' option in System Preferences > Security & Privacy again! That was a long wait, but this option work again thankfully. Huge time saver!!!

I also have this issue since upgrading to Big Sur. My Apple Watch (series 4, latest iOS) has worked seamlessly with other operating systems but just refuses to connect to my watch.

I've tried all of the suggestions in this thread but to no avail.

Hoping Apple fix this soon as it's a very useful feature.

None of what I've seen on this thread works. Back in old days, there was a quaint custom of *TESTING* software before rolling it out. But I guess that's out of fashion now. Better to just use your customers as guinea pigs.

My Apple Watch will not unlock my iMac after Big Sur as well. When I went to the Security & Privacy section in settings I saw that the box was checked to "Use you Apple Watch to unlock apps and your Mac". I unlocked the section then unchecked the box but upon trying to recheck the box I get the following Error.

"Your Mac was unable to Communicate with your Apple Watch. " Even though the watch was unlocked, on my wrist, and powered on.

I finally got it to work, but only after doing a reset on the watch, which is basically erasing all its content and settings, unpairing it from the from the phone, then pairing it agains and restoring it from the backup on the phone.

I can't wait to see what other surprises Big Sur has for me.

Thanks a lot. That procede worked for me too

its much easier and faster than one might think. I did a restart of the Mac and checked/unchecked „unlock with Apple Watch „ 2 or 3 times.

important: before you check the box , you have to unlock your iPhone ! Otherwise you get an error that the watch could not be connected.

than I had to wait some minutes for the watch to work.

This solved my problem. It's rather laborious, took me almost half an hour, not all watch settings were restored from backup, but it appears the unlock is working again. I hope I'm out of the woods because this Watch Unlock thing has been brittle since the beginning.

Series 5. Kept getting an error when checking “Unlock with Apple Watch.” I unpaired the  Watch and then restored from backup and it now unlocks the Mac running Big Sur and will let me approve passwords from the  Watch.