On the voice control panel, single press BOTTOM KEY to turn on Voice Control.
Another single press to switch between start and stop. Long press top key to exit the menu.
This feature is available with IOS 7 + devices that support Siri and select Android 4.3 + that support Google Now or S Voice.
TIPS: To use voice control, your smartphone must have access to the internet using either 3/4g or WIFI.