Apple has warned owners of its new iPhone 13 model that they might not be able unlock their phone with an Apple Watch due to a software glitch.

The good news is that Apple is lining up a software update that should resolve the problem, according to a new support document.

"You might see "Unable to Communicate with Apple Watch" if you try to unlock your iPhone while wearing a face mask, or you might not be able to set up Unlock with Apple Watch," Apple notes.

It says this will be fixed in an upcoming software update.

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Until the update is available, users can turn off Unlock with Apple Watch and use a passcode to unlock an iPhone 13. Users need to go to Settings > Face ID & Passcode.

Apple created the Watch unlock feature for the iPhone in response to Face ID being obstructed by people wearing face masks. Instead of glancing at the iPhone's facial recognition camera sensors, a nearby Watch that's being worn and unlocked, can unlock the iPhone. A similar feature is available for macOS devices.

Your Apple Watch might not unlock your iPhone 13, but a fix is coming

The feature is handy for users with an iPhone and Apple Watch but it has had problems before on older iPhones with Touch ID. This only affected enterprise users.

Otherwise, the feature requires an iPhone that uses Face ID, including iPhone X or later, and is running iOS 14.5 or later. The person needs an Apple Watch Series 3 or later with watchOS 7.4 or later.

The Watch also needs to be paired with an iPhone and both the iPhone and Apple Watch need to have Wi-Fi and Bluetooth on.

Face ID fails when users have a mask that covers a person's nose and mouth. The Watch side of the unlock requires wrist detection to be enabled.

There is a security concern with the process as it can mean users accidentally unlock an iPhone. This can create an additional step if the phone is confirmed to have been accidentally unlocked by a Watch.

"When your Apple Watch unlocks your iPhone successfully, your watch gives haptic feedback and shows an alert. If you didn't mean to unlock your iPhone, tap the Lock iPhone button on your Apple Watch screen," Apple notes.

"Next time you unlock your iPhone after tapping this button, your iPhone will need you to enter your passcode."

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It's not clear when Apple will release the update to fix the issue or what version of iOS it will come in. MacRumors notes that the first beta of iOS 15.1 was released last week, but Apple may release a minor iOS 15.0.1 update with bug fixes.

Apple released the iPhone 13 earlier this month. It's available with 128GB, 256GB or 512GB. Pricing starts at $699 for the iPhone 13 Mini or $799 for the iPhone 13.