control word for speech recognition

I want my speech - enabled winforms application to have a control word to which it responds.
In other words, it monitors my speech for this word and only responds if it "hears" it, then enabled additional commands.   It seems like this approach will require two instances of the speech class, one that listens for the control word and another for the remaining commands.

Am I on the right track, or is there a better approach?

Thanks