Soon, you'll be able to command 'OK Google' to search in third-party apps

Rather than having to search through apps like Yelp, soon you'll be able to simply wake up your phone with the "OK, Google" command that's baked into Google Search and use your voice to search useful information. Once developers update their apps with just a few short lines of code that Google is allowing, you'll be able to perform voice searches like "Ok, Google. Find me the nearest pizza place on Yelp" all without having to touch your screen.

source: androidcentral