Looks like you have to press a button for it to start listening.

You can unplug it.

I'm sure they'll allow you to disable Siri though (or maybe even disable the "hey Siri" crap and just use a button or something).

On the iPhone, the always-on "Hey Siri" activation is actually local on the device. You can test this out by activating Airplane Mode and saying "Hey Siri". The interface comes up, then says that you can't use Siri because you're offline.

This means that Apple isn't listening to you 24/7, only when Siri is activated. Sure, sometimes it's activated accidentally and might overhear something you didn't want it to, but those times are pretty rare.

If Apple introduces a "Hey Siri" feature on the Mac (which it's unclear about given the fact that in the demo Craig activated Siri by clicking on the icon, then later by pressing a key on the keyboard), I expect it would operate in the same way.

Finally, I'm sure there's a software setting you can use to disable Siri if you really don't want it to be activated.

I wonder if this will work similarly to pressing Fn twice to get to get the speech-to-text dialog in OSX.