Just say "Ok Google"
Google Voice Search has been slowly rolling out to the Google Chrome browser for some time now, and now the beta version is just listening for your command. The listening search box is present on Google.com and in new blank tabs, and just like with the Google Now Launcher it is always listening for the command "Ok Google". Say that and Google Voice Search springs to life, waiting for you to perform a search, set a timer, or whatever else it is you want to do through Google.
The latest beta version has the option enabled, though according to the Google Chrome Blog the feature "will be rolled out to English (U.S.) users on Windows, Mac and Linux over the next few days, with support for additional languages and Chrome OS coming soon."
All you need is the latest Chrome beta for your hands-free Googling, and you can download that right here
Source: Google Chrome Blog