I\'m building an app that uses Voice Commands to perform certain functions. I got some codes working from here
private static final int SPEECH_REQUEST_CODE = 0;
Continuous Speech recognition with help of Service :-
Android Speech Recognition as a service on Android 4.1 & 4.2
GitHub Sample :-
https://github.com/galrom/ContinuesVoiceRecognition
Responding to magic words like Ok Google
https://github.com/cmusphinx/pocketsphinx-android-demo
I have implemented same feature for Banking Project. I was triggering speech to text recognition on device shake
You will need to write a service for continuous speech recognition. And based on the inputs you get as speech detect your trigger phrase and take action.
This may be memory intensive and you will need to optimize by starting and stopping services on appropriate times and screens.
The accepted answer to this question provides a means to achieve a similar thing.