Ok Google will work from the lock screen. If no security is set up than it will work ONLY if plugged in. If security is set up, password, figure print, etc, than you also have to setup your voice as a trusted device. And it still must be plugged in to a power source.
I do remember there is an app that allows you to use S Voice to activate Google Search. S Voice can work from the lock screen without being plugged in. It was clumsy but it worked.