A little tip worth pointing out for new Samsung Galaxy S5 owners, that the "OK Google" hotword works out of the box in the new Touchwiz launcher. It may seem obvious to some, but having spoken to a few people in the past couple of days that didn't know about it, it's worth highlighting.
It's actually the Google Search widget that takes care of things, and this is preloaded onto the homescreen when you first fire up the phone. So, without any additional downloads, just say "OK Google" while on the main homescreen. From there take advantage of the voice activated benefits it brings with it such as setting alarms, set some music off playing and, well, searching the web. Piece of cake!
OK Google isn't supported everywhere just yet, but if you're in a country that does you shouldn't have any problems putting it to use on the Galaxy S5.