Nexus 5 and Samsung Galaxy S5 users are currently limited to using the "Ok Google" command on the homescreen of their devices. But Google is reportedly working on a way to bring the voice command feature everywhere on your Android device. Similar to what the Moto X does, your device will listen and respond to your voice and respond to what you have running. For example, if you are looking through photos, you can tell Google to "share this photo" with someone. It is still a rumour at the moment but an extremely handy feature if ever it does get confirmed.

Source: Engadget