The latest version of Google Search is spreading the reach of the “Ok Google” voice command deeper into Android and its apps. In versions before 3.5.14, the voice command only worked on the home screen but the latest version makes it possible to use it wherever you are and that even includes the lock screen.
Note that the new setting is not enabled by default so you may need to go into your settings to turn it on. Simply go to the Google Search app and scroll to the bottom then click on Settings > Voice > ”’Ok Google’ hotword detection” and toggle on the settings you want. Among these are ‘From Google Search app,’ ‘From any screen,’ and ‘From lock screen.’ With everything enabled, “Ok Google” will work from any screen.
The new version also comes with a new Audio History feature that saves the commands you’ve given in the past. It uses the information to learn the sound of your voice, improve speech recognition and lean how you pronounce words and phrases.
There are a couple of caveats: You must have Android 4.3 or higher and the Audio History setting must be turned on. Google also indicates that it only works for English speakers in the United States. If you cannot get it to work, you may need to change your region settings.
Note that you can also opt out if you find that Google is paying a little too much attention to everything you say!
Source : Google Play