You have to double tap Home Button to access S Voice. In case you have disabled it by mistake you can also access it through the settings> toolbox option .
Just got an S5 after a happy year with an S4, pretty happy with it except for one major item. There appears to be no way to start S Voice from the lock screen by saying "Hi Galaxy" like I could on the S4. There is no "Voice Command" option in "Settings",or at least I can't find it. This also makes it where I can't turn off an alarm by voice or hit snooze. Am I just missing it or did Samsung delete some very cool functionality here?

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