"OK Google" is creeping into every corner of Google services. First, the Google Now launch phrase was limited only to the homescreen on Android 4.4 KitKat devices but now the voice-activated command will soon be available on any screen, any app and even on the lockscreen of your Android smartphone or tablet. Google is also including a Audio History feature which learns from your voice searches to make detection better.
All these features are coming as a part of the Google Search app update 3.5.14, which is being rolled out on a phone-by-phone basis. If you are eligible then you can simply go to Google Search settings and look inside the "OK Google Detection" menu.
Source: Droid Life
