Your Mac was unable to communicate with your Apple Watch.

Yay! This worked (after trying all the other stuff that did not work!). Why are we so obsessed with making little things like this work?! I mean, typing my login password takes about 1/2 a second! I spent 3 hours troubleshooting this! Whats wrong with us???

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.

Had the same problem plus the handoff function didn't work after upgrade to Big Sur. After contacting support the problem has been solved after the first step they recommended to find out if the problem is related to the MacBook or iCloud account. Here is what I did step by step, I suppose some steps are not needed, I wt trying different things:

• Support asked me to check if the problem appears if I create a new user account in MacOS. So I created a new test user in MacOS (in my case it wasn't even an admin user, so restart was not required) with minimum required configuration (I skipped all steps that were not necessary like touchID config.)
• log in to this new user account, setup iCloud for this new account
• turn on "unlock with Apple Watch" function settings
• turned out that both handoff function and this one work properly for this new account - so I know the problem is not related to the hardware
• log in back to the original MacOS account - here I checked iCloud settings, logged out from the iCloud (worked after few attempts due to pending picture synchronisation)
• restart
• enabling "Use your Apple Watch to unlock apps and your Mac." - it worked after 2nd or maybe 3rd attempt, I'm not sure but definitely the 1st attempt resulted in the same error message the story has started from
• fixed! :) And also handoff works properly with my watch and iPhone

Hope it can help others to fix the issue!

@hakarlmedskyr I had the same error message - "Your Mac was unable to communicate with your Apple Watch."

I initially got the message that my watch needed to be signed in to my iCloud account - which it definitely was.

So, I also followed other suggestions to try to get the watch to unlock my Mac:

• Signed out of iCloud on my Mac
• Shut down
• Restarted my Mac (M1 MacBook Air, Big Sur v11.2.3)
• Went to System Preferences -> Security & Privacy -> Use your Apple Watch to unlock apps and your Mac

At least I didn't get the "Your watch must be signed into your iCloud message"…

However, I got the "Your Mac was unable to communicate with your Apple Watch." message. Here are the next steps I took:

• I made sure my watch (Series 4) was on the same WiFi network as my iPhone 11 and Mac
• Made a phone call from my watch
• I left a voicemail at the number I called from my watch (just wanted to make sure that my watch was actually connected to my phone, and also that the watch actually making the call)
• I went back to System Preferences -> Security & Privacy -> Use you Apple Watch to unlock apps and your Mac and checked the box (to unlock apps and Mac)

Then it worked!

I hope that helps someone.

I got the same problem for months.

The approach with "Keychain Access" doesn't work for my case as I couldn't find the "View" and "Show Invisible Items" at all. I even tried to reset my Apple watch (series 3), as well as upgrade the OS on the watch (7.3.2) and my MacBook (Big Sur), but it still doesn't work either.

After a few search on the Internet, I just found another solution that works for me, so you can give it a try. Here it is:

1. On your iPhone, go to the Watch app
2. Go to the passcode section
3. Switch off the "Unlock with iPhone" toggle
4. On your Macbook, go to System Preferences > Security & Privacy
5. Tick on "Use your Apple Watch to unlock your apps and your Mac" (and it now should be working fine)
6. Back to iPhone and switch on the "Unlock with iPhone" toggle (optional, if you want to keep the "unlock Apple Watch by iPhone" feature)

My hypothesis is that Apple doesn't want users to use iPhone to unlock MacBooks (I don't know why).

After a couple of days of it remaining flakey I decided to go nuclear and restore my iPhone 10 from scratch to the just realized 14.6 . It worked.

Even better.... It also resolved the bad battery drain (drained in 24hours with zero use) issue I had since 14 came along. This had also defied the myriad suggestions to fix (including a full restore) and seemed to be caused by background activities (mainly apple) that refused to turn off. Inspired by this I did a full restore to my IPadPro 11 which then cleaned up its battery drain as well. What makes this even more curious is yesterday there were reports of battery drain being caused by 14.6.

Steps

1. Backup iPhone to iCloud
2. Connect iPhone to Mac via finder
3. Initiate restore (ie update to 14.6) from the Mac (not via Wifi)
4. Restore backup via iCloud (wifi)
5. Update iWatch to 7.5
6. Re-pair iWatch and iPhone
7. On Mac preferences - security - "Use Apple watch..." turn it off then on again
8. Check handoff is on and same wifi on iPhone, iWatch and Mac.

I'm having the same problem.

In my case I had been using my Apple Watch 5 successfully to unlock my MacBook Air (purchased within the year) and 27" iMac (also purchased this year).

When the new phone, iPad, and watch updates were released last week, I installed them on my phone and iPad (probably not relevant here) and Watch. After the update the watch was burning through battery power at a high rate — where before I would end a day with maybe 30% left, now it was running out of juice by late afternoon. To resolve this problem I finally read that I might need to unpair and repair my watch and phone, which I did.

After successfully repairing watch and phone the watch no longer would unlock my Air and iMac. On both Macs I went into the Security & Privacy Control Panel and checked the box to "Use your Apple Watch to unlock apps and your Mac." The Macs would spin their wheels for perhaps a minute and then I get the "Your Mac was unable to communicate with your Apple Watch" message.

I rebooted the watch and the computers and the problem persists.

Same issue here - after having to repair a Series 5 due to excessive battery drain. Tried this suggestion, did not help - receiving same error message - "Your Mac was unable to communicate with your Apple Watch."

This is unacceptable for an OS upgrade ( on any device ) that it renders both the normal operation and advertised features useless. Disappointed with Apple on this one.

I had the option enabled and after updating to iOS14 and watchOS7, the auto unlocking screen stopped working. However, the Apple Watch side button to auto-type system password was working fine. The moment when I toggled that Checkbox, it is never enabled ever since. This is definitely an issue post the latest update!

Apple seem least bothered as about 10% of the Apple user are aware, that such a feature even exists. :-P

Same here; after unpairing and pairing a Series 4 Watch due to poor battery life after WatchOs 7 upgrade I cannot use the watch to unlock my MacBook - "Your Mac was unable to communicate with your Apple Watch."

I have exactly the same issue with Watch os7 and Mac 10.15.7 after updates and then re-pairing watch and iPhone (because of battery drain).

called Apple support who said “it is with engineering now”!

would welcome any more advice....

Brilliant mark__t that fix worked a treat, seems the watch updating to os7 and having to be re-paired with the phone, upsets the keys for the watch in keychain on the mac, so deleting the old files works perfectly.

I have exactly the same situation going on here -- and I've gone through all of the "fixes" that seemed to have worked for one person or another, but not me. I even went thru one suggestion of deleting the entries from the ~/Library/Sharing/AutoUnlock...blah, blah. Still, nope.

It is frustrating, and I've pretty much given up. I'll just enter the password on my Mac and move on until Apple gets off their duffs and fixes the problem (for good).

At least the unpair / pair my watch to my phone and starting from scratch (not from backup) worked to fix my horrible battery life after the update! However, the battery is still not as good as before the update -- but, a heck of a lot better.

Funny, my husband has NOT experienced any issues after the update.

Unbelievable!

After posting (a few mins ago), I did the 'ol "grins and giggles" of trying to enable unlock the mac with my watch option (for the umpteenth time) AND IT WORKED!

I tried the enable option just after doing the file deletions (at least 3-4 times) and it didn't work. After submitting my post, I decided to give it one more try and it worked! It must have been like a 3-5 min wait between last fail and when it succeeded. Go figure.

Thanks!

Now here a funny (annoying) situation. Having fixed the issue as per the post above of deleting .plist files etc etc.

It worked! well for a couple of times. But figure this one...

Walk away for 30 mins to make a cup of tea, so the mac loses sight of the watch and, on your return to the mac it doesn't work again until you reset the tick box in system preferences...

Something is upsetting the keychain files i guess?? reset the flag and file sand all works again...

any ideas?