Auto-Unlock on a manually Continuity-enabled Mac?
What hardware is required for Auto Unlock?
According to Apple’s macOS Sierra beta 2 release notes, Auto Lock requires a 2013 or later Mac. That means that even 2012 Macs with Bluetooth 4.0 don’t officially support Auto Unlock.
What software is required for Auto Unlock?
To use Auto Unlock, you’ll need to be running macOS Sierra Developer Preview Seed 2. You’ll also need to have the watchOS 3 beta installed on your Apple Watch. Apple indicates that the latest version of watchOS 3 (beta 2) needs to be installed, but I was able to get Auto Unlock working with watchOS 3 beta 1.
You’ll also need to have Two-Factor Authentication established for the iCloud account associated with your Mac and Apple Watch.
How do I set up Two-Factor Authentication?
Two-Factor Authentication can be set up via the Apple ID website. Beware that a small number of users are complaining of being locked out of their accounts when enabling 2FA on the developer beta.
Keep in mind that Two-Factor Authentication differs from Two-Step Authentication. You must be using Two-Factor Authentication for Auto Unlock to work. If you need assistance, a full guide for enabling Two-Factor Authentication.
Once 2FA is enabled, Apple encourages users to do the following:

On your Mac, open System Preferences →  iCloud, and click the Account
Details button. Click the Security tab, and make sure Two-Factor
Authentication is on. On your iPhone, open Settings →  iCloud and tap
on your name to reveal account details. Tap on the Password and
Security item, and make sure sure Two-Factor Authentication is on.
On your iPhone, open Watch →  General →  Apple ID, and verify your
Apple ID is showing.
How do I enable Auto Unlock?

Enabling Auto Unlock is handled on your Mac via System Preferences → Security &amp; Privacy.
I’m not seeing the Auto Unlock setting in System Preferences
After performing a clean install, it can take minutes for the Allow your Apple Watch to unlock your Mac checkbox to display in System Preferences → Security and Privacy → General on your Mac. This delay occurs while your devices are iCloud pairing. If you performed an upgrade instead of a clean install, you should not experience any delays.
If you’re still having problems getting Auto Unlock to work, try rebooting all three devices (Mac, Apple Watch, paired iPhone). Also, double-check to make sure you have Two-Factor Authentication enabled, not Two-Step Authentication.