The "Ok Google" hotword is a pretty nice little feature to help streamline use of voice commands with Google Now. We first saw an iteration of this implemented withing Google Glass, to help with the functionality of the smart eye wear since there is no way to type in what you want the device to do, although the hotword for glass was slightly different in that you would tell your device "OK Glass" instead. The Ok Google feature has since only been available with the Nexus 5 when it comes to smartphones, as well as also being included in with some functionality on Chromebooks. You also have a similar function on the Moto X, although it's not as diverse in it's uses. The feature is all told pretty useful and there are many phones out there that would benefit from it.
Thanks to the development community, we often see features like this come to other devices that otherwise weren't mean to have the features implemented. Because of the hard work from one developer by the name of memnoc over at the XDA forums, this "OK Google" hotword feature can now be installed and used on any device, and supports multiple languages as well. If you have been wishing and waiting for Google to implement this feature to your device on their own, there's no longer a need to wait as you can have the feature available in a minimal amount of time. Like most things that come our way via XDA, you're phone will have to be rooted for this to work, and you'll want a file explorer of some kind to work with the files that you'll have to download. The other requirements are that your phone or device be running the latest version of Kit Kat which is 4.4.2, and the feature is said to work with all ROMs including those that are not based of the Android Open Source Project(AOSP). If you want to get this little function onto your phone as soon as possible, head over to the original forum for all the instructions, as the process doesn't seem like it'll take much time at all to get things going.