I can't seem to active S Voice from anywhere (Lock Screen with no pin, Home Screen, any app) on my Galaxy S5 (ATT). I have the Wake On command set. I've tried changing from Hi Galaxy to a different command. I cleared S Voice cache data and restarted and still no luck. I'm using the Google Launcher but also switched back to Touchwiz and neither work.
I've noticed others are having the same issue. http://forums.androidcentral.com/samsung-galaxy-s5/379600-galaxy-s5-hi-galaxy-not-working-sm-g900i.html