Developers will have to add code for the same to their apps before this gets functional and once this becomes a popular thing, Google Now will become even handier tool. For instance, if you like a particular dictionary app, you can trigger Google Now from any screen and say “ Search Machiavellianism on XYZ App” and your phone will take you to the word meaning in particular dictionary app you spoke. Similarly whenever you need to use search feature of any Android app like Zomato, YouTube, etc you can directly access it via Google Now “How many lines of code will it take to let your users say Ok Google, and search for something in your app? Hardly any. Starting today, all you need is a small addition to your AndroidManifest.xml in order to connect the Google Now SEARCH_ACTION with your searchable activity,” wrote Jarek Wilkiewicz, Developer Advocate, Google Search, in a post on Android Developers blog.] For now, the feature will work in English language on all Android 4.2 Jelly bean or newer devices with Google App v3.5 or later. Source