Now, thanks to the newest update to Google voice search, I can just say "Ok, google" even from the lock screen. Even if I'm in an app. Even if the screen is off but the phone is plugged in. Just say the magic words and I hear that magic binging noise, ready to answer my every question.
Yes, yes, I know that the Moto X has had this capability for a little while now. I'm over that. We're all getting it now, and I hope everyone enjoys it.
To enable, open the "Google" app, which is where you find your Google Now cards. Click on the menu button, go to setting, then voice. Then, click on the "Ok Google" detection where you can adjust the settings.
Now, be warned, enabling this means your phone is going to be listening to you. Most of the time in fact. And it's going to send information to Google about your searches and voice. For the privacy concerned, you should be aware of this. However, Google already knows a lot about me since I use an Android phone, Gmail, and most of their other services. As for me, I enabled it all as soon as possible and have been loving it.