Android : Block System Dialog box from a service Android

I would like to block the system pop up dialog box from a service, the one which appears when we long press the power button. I using below code to block it from an activity

@Override
    public void onWindowFocusChanged(boolean hasFocus) {
        super.onWindowFocusChanged(hasFocus);

       if (!hasFocus) {
             Intent closeDialog = new Intent(Intent.ACTION_CLOSE_SYSTEM_DIALOGS);
            sendBroadcast(closeDialog);
        }
    }

But I want to do it in a service since I want to block it even if the app is closed.