Siri for Mac: How it works in Apple's macOS Sierra and what it's capable of
macOS Sierra, revealed during Apple's WWDC keynote on Monday, will be the first Mac operating system to include Siri. Although many people are familiar with how the virtual assistant works in iOS, there will be quite a few differences on desktops and laptops.

On current Mac models, at least, the main way you'll trigger it is by clicking on a new Dock icon, although during the keynote, a keyboard shortcut also seemed to be available. In any case, there will be a Menu Bar icon in the upper right.
Macs will have access to just about every Siri function present on iOS devices, with the obvious exception of anything hardware-specific. Among options will be things like reminders, photo browsing, Apple Music, FaceTime calls, restaurant reservations, and finding movie times and sports scores.
Where the Mac will come into its own, though, is integration with Finder. Although opening the app itself may be easier for locating specific files, Siri will allow searches according to broad criteria like when files were last opened or who sent them. The system will moreover support contextual follow-up commands, which can narrow down results.

People will also be able to export Siri content for the first time. When searching the Web for an image or a Maps location for instance, that content can be dragged and dropped directly into another application. Siri results can additionally be pinned to the Today tab in the Notification Center, where they'll be updated automatically if there are any changes.

Apple has hinted at other Mac-specific commands as well, such as the ability to check how much free storage space is left.
Something that remains to be seen is how the Siri SDK might open up third-party app functionality. Apple concentrated on how it would improve iOS apps during its keynote, but the technology could become even more useful given the greater scope and power of desktop software.

On current Mac models, at least, the main way you'll trigger it is by clicking on a new Dock icon, although during the keynote, a keyboard shortcut also seemed to be available. In any case, there will be a Menu Bar icon in the upper right.
Macs will have access to just about every Siri function present on iOS devices, with the obvious exception of anything hardware-specific. Among options will be things like reminders, photo browsing, Apple Music, FaceTime calls, restaurant reservations, and finding movie times and sports scores.
Where the Mac will come into its own, though, is integration with Finder. Although opening the app itself may be easier for locating specific files, Siri will allow searches according to broad criteria like when files were last opened or who sent them. The system will moreover support contextual follow-up commands, which can narrow down results.

People will also be able to export Siri content for the first time. When searching the Web for an image or a Maps location for instance, that content can be dragged and dropped directly into another application. Siri results can additionally be pinned to the Today tab in the Notification Center, where they'll be updated automatically if there are any changes.

Apple has hinted at other Mac-specific commands as well, such as the ability to check how much free storage space is left.
Something that remains to be seen is how the Siri SDK might open up third-party app functionality. Apple concentrated on how it would improve iOS apps during its keynote, but the technology could become even more useful given the greater scope and power of desktop software.
Comments
I'm sure there will be an option for it. "Dictation Commands" has always had on "always on" option by saying a specified phrase (Default is, "Computer" - I have it set to, "can you"), so there's no reason Siri won't as well.
This is a Mac. You use a Mac with a keyboard and mouse/trackpad. Your hands are already on either if you are using the product. For me, the keyboard shortcut of Function Space just became part of my new routine. For others, one of the two icons on the screen will suffice.
Anything else is honestly slower, and unneeded.
Well, then you don't want Siri.
It's apparent that you don't see the value in having such a feature, and as such YOU never have to use it. But there are people with more active imaginations that see the potential in it. For instance, my iMac is in my bedroom and it doubles as my "entertainment center". It would be very nice if I could tell it a multitude of commands to control media playback from my bed at night.
Furthermore, having a second form of input would allow users to become truly "multi-tasking". While you're typing away on something, you could simply ask Siri to look something up for you without needing to break away from what you're typing. It's like having an assistant to do mundane tasks without you needing to drop focus on what you're doing.
And what about multiple people sitting around a desk, and someone says "Hey Siri" and all computers suddenly execute the command. Although I suppose that same problem affects phones, too.
But more to the point, Siri is *crying out* to be integrated with Spotlight. Why on earth would these remain on parallel tracks?
I dunno about siri but with Cortana you can train her to learn your voice so she only responds to your "hey Cortana". I've tried it and it works pretty well
Siri is trainable. I can fool her and access my wife's iPhone but my wife cannot fool Siri on my iPhone. Must be all that falsetto karaoke I do.
Siri had access to all spotlight files and functions at the WWDC demo so what's the difference?