系統本身有這個廣播，只需要監聽這個廣播就可以了！

    private BroadcastReceiver mHomeKeyEventReceiver = new BroadcastReceiver() {
        String SYSTEM_REASON = "reason";
        String SYSTEM_HOME_KEY = "homekey";
        String SYSTEM_HOME_KEY_LONG = "recentapps";

        @Override
        public void onReceive(Context context, 
 
Intent intent) {
            String action = intent.getAction();
            if (action.equals(Intent.ACTION_CLOSE_SYSTEM_DIALOGS)) {
                String reason = intent.getStringExtra(SYSTEM_REASON);
                if (TextUtils.equals(reason, SYSTEM_HOME_KEY)) {
                    //表示按了home鍵,程式到了後臺
 
//                    showShortToast("按了home鍵,程式到了後臺");
                } 
            }
        }
    };

//註冊廣播
registerReceiver(mHomeKeyEventReceiver, new IntentFilter(Intent.ACTION_CLOSE_SYSTEM_DIALOGS));

這樣，在手機按下Home鍵時，可以做想要的操作。