How to check if a Mac Supports Auto Unlock with the Apple Watch

There are three documents listing the requirements for the Auto Unlock of a Mac using the Apple Watch, with conflicting information.

• The Apple Watch User Guide (https://help.apple.com/watch/#/apd4200675b8) says "Mac (2013 or later) with macOS Sierra",
• This support document Automatically unlock your Mac with your Apple Watch - Apple Support is more specefic and says "mid-2013 or newer Mac model".
• The most specific list is here, however:

System requirements for Continuity on Mac, iPhone, iPad, iPod touch, and Apple Watch - Apple Support

The Mac Help points out a way to check this using the System Information:
"System Information can confirm if your Mac supports Auto Unlock. Choose Apple menu > About This Mac, then click System Report. In the sidebar, click Network, click Wi-Fi, then look in the Interfaces section for Auto Unlock."

So, when in doubt, look at the system profile  > About This Mac, System Report and check the Network > Wi-Fi section, if the the installed card type for your network supports the Auto Unlock feature.

A frequently reported problem is, that the setting to "Allow Apple Watch to unlock the computer" suddenly vanishes from the System Preferences, after the users changed from two-step authentication to two-factor authentication as required for the unlock feature.

The Help for System Preferences lists, that the unlock feature will be hidden, if the watch is not paired with its iPhone, even if the computer should support this feature.

So check, if your watch is still paired with its iPhone, and also check, if Bluetooth is still enabled on the Mac and the watch, if you no longer see this setting in the System Preferences.