public boolean onKeyDown(int keyCode, KeyEvent event) { 
    if (keyCode == KeyEvent.KEYCODE_BACK) { 
        Intent intent = new Intent(Intent.ACTION_MAIN); 
        intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK); 
        intent.addCategory(Intent.CATEGORY_HOME); 
        startActivity(intent); 
        return true; 
    } 
    return super.onKeyDown(keyCode, event); 
}