S Voice as your intelligent assistance on your Samsung Galaxy devices (S2, S3) can be opened and used by either going to App drawer and rapping S voice or just Double Pressing the Home Button. If you have already defined enabled "Wake Up Commands", you may Wake up S Voice by saying "Hi, Galaxy".
If you want to disable opening S Voice with the mentioned ways, do as follows:
1. To disable Opening S Voice by double pressing the Home key, Open S Voice, Press Menu button and select Settings, make sure to unmark "Open via the home key"
2. To disable Auto wake up by commands, make sure to unmark "Wake up command" in the settings menu.