Google have brought automated voice search functionality directly to the Chrome browser. The feature was limited to a number of Android devices but it looks like Google is expanding, now bringing to your desktop.
Whenever you say 'Ok Google', it'll recognise the hotword and you can then say your query. You'll be presented with relevant results, just as you would normally when using voice search.
To use it though, you need to be on the google.com homepage. You can't use the regional sites such as google.co.uk. You can unfortunately use it in a new tab as of yet. And I've found that if you have multiple applications open, you need to be on Chrome for it to work - you can't be using another application and use the hotword functionality. It kind of defeats the process of automation. But Google may have bigger plans up its sleeve.