“Ok Google” is the expression that triggers voice commands on Android devices and Google Glass. The expression was previously limited to the home screen of Android 4.4 KitKat on the Moto X, but now the voice-activated command will soon be enabled on any screen, including the lockscreen on smartphones and tablets.
Google is including a new Audio History feature that learns the sound of your voice to increase the accuracy of searches.
This feature will be a part of the Google Search app on a phone-by-phone basis. If you are eligible for the feature, navigate to your Google Now settings and enable the options inside the “OK Google Detection” menu.