@Override
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);
        this.startActivity(intent);
        return true
 
;
    } else {
        return super.onKeyDown(keyCode, event);
    }

}