Google recently released a Chrome extension that will make voice search automatic, just like how it is in the browser’s mobile version. Previously, using the audio search feature on Chrome for desktop requires clicking on a button before one can start speaking. With the new Chrome extension, audio search is now automatic, and can in fact be triggered with the words “Okay, Google”.
For the automatic audio search feature to work, the Chrome browser has to be pointed to google.com and the Google search page has to be the active tab. The feature works on any search results page as well. Check out the Chrome extension here.