Cortana, Microsoft's intelligent assistant listens out for your voice, so you can quickly jump into a search, but by default it will respond to anyone who shouts out 'Hey Cortana'. You can set it up to only recognize your dulcet tones though, just click on the Cortana box, go to the 'Settings' page and toggle the 'Respond Best To Me' slider.
Now, Cortana will attempt to learn your voice. She'll give you six phrases to repeat. Once that's done, and it might take a few attempts, you'll have the sassy personal assistant all to yourself.
