Android : background service for voice command

i need to use a background service to lunch my application with voice command even the screen is locked , for example when i say "start" the screen will be unlocked and the application lunch automatically , it is the first application for me , i tried to make this code work https://github.com/gast-lib/gast-lib/blob/master/library/src/root/gast/speech/activation/SpeechActivationService.java but i don't know how to use that and how to do the service with the activity .