UPDATE MAY 3rd
Please see this post for more up-to-date information regarding OK Google coming to desktops for non-US users.
UPDATE FEB 27th
The Chrome blog today announced that this feature will start rolling out to beta users in the next few days starting with US users and will be followed up soon with support for ChromeOS and other languages.
Recently you may have read about or used the Google Voice Search Hotword (Beta) extension for Chrome. If you haven't then basically it is an extension that allows you to use the 'OK Google' hotword to activate searches on Google (currently only available on .com) using your desktop/laptop computer.
Google appear to have taken the functionality of this extension and integrated it into Chrome.
With the original extension enabled you see 'Say "OK Google"' appear in Google's searchbox. This indicated that the extension was listening for you to say the hotword and start a search/ask a question. A feature mobile users of the Google search app are well aware of, even though it was only available if you had the US language selected in settings (unless you used this OK Google Hotword workaround).
We have known for a while that Google was looking to intergrate this into their Chrome browser as it was showcased in the 2013 Google I/O.
It looks like this is coming closer to being a default setting, currently it is hidden behind a flag. At the time of writing it can only be enabled on the more recent versions of Canary & Chromium.
The flag is not available at the usual chrome://flags
so you will need to launch Canary/Chromium via Terminal using the following switch
/Applications/Google\ Chrome\ Canary.app/Contents/MacOS/Google\ Chrome\ Canary --force-fieldtrials=VoiceTrigger/abc/
/Applications/Chromium.app/Contents/MacOS/Chromium --force-fieldtrials=VoiceTrigger/abc/
Once you have done this you need to open Chrome Canary settings (CMD+,). Once this opens look for the Search section in settings and select 'Enable "Ok Google" to start a voice search'.
After selecting enable you will see a couple of other options which can be seen in the screenshot below.
So I expect to see this as a native feature for the stable releases sometime soon-ish and hopefully working on more than just .com as it currently does.
As this is on Canary there are bugs and it is not working as it should. This really just shows that is there and something that Google will bring to us soon. If you really want to try it out then I would recommend the aforementioned extension as this works fine.
On a side note the flag may currently be hidden whilst Google try and fix a bug which could allow shady websites/organisations to continue recording whatever you are saying long after you have left their website. For more reading on that please read this article over at Tal Ater.