(Nuance/Apple Siri, Microsoft Cortana, Google Now, IBM Watson Speech, Amazon Echo, LG-Smart TV, etc.)
From a consumer perspective you want an offline speech product like Nuance Dragon NaturallySpeaking: http://en.wikipedia.org/wiki/Dragon_NaturallySpeaking (it's the same technology that powers Nuance cloud based products like Apple Siri, IBM Watson, etc.)
But, if anyone commenting had actually used one of the new samsung smart TV's with this feature, you'd see that this is being blown out of proportion.
The TV isn't even listening for a keyword. It's waiting for you to press a button on the remote. The microphone for voice control is actually in the remote itself.
Samsung Smart TV remote with Voice button: http://goo.gl/DkgWPb
I would caveat the above by saying that the TV may also have a microphone in it, because I have noticed that when you use the built-in skype app, the camera does a cool digital/zoom to highlight whoever is speaking, which it probably does either with a microphone array, or moving-lips detection in the camera. The camera, by the way, can be physically disabled when not in use, by pushing it into the TV.
The non-remote one does use a trigger word ("hi tv" by default) and it definitely does that processing locally (I know because i disconnected my TV from the internet and tried it). Basic commands ("channel up" etc) also worked. I don't know what else to try to figure out when it goes out to the internet. I'd also add that the camera/microphone have a very visible hardware off (which I keep off, because life is too much like 1984 already).
Again, this is a 2013 model.