For the feature to work, the Apple Watch must be unlocked—meaning you’ve entered in the passcode or unlocked your phone, and it’s been continuously attached to your wrist since then.
The Mac needs to have Wi-Fi and Bluetooth enabled and be released in 2013 or later.
Speech-to-text dictation is still a feature, but it’s not connected to Siri in any way—it’s been relocated to the Keyboard preference pane, in fact.
The strengths and weaknesses of Siri on i OS are still in evidence on mac OS.
Version 10.12 of the operating system that runs the Mac is here, and with it, a new/old name: mac OS.
Though the name has changed, mac OS Sierra follows Apple’s Mac gameplan of recent years, adding features in sync with updates to i OS, and expansion of i Cloud integration.
You can use Siri to launch Apple Script or Automator apps, but there’s no real integration—they’re just launched like any other app.
In general, Siri on the Mac does exactly what Apple intended it to do: It provides people who are familiar with Siri on i OS with pretty much what they’d expect.