播放一段特效聲音，例如鈴音，可以在點擊按鈕德時候調用 playSound()

		
	private void playSound(){

        MediaPlayer mediaPlayer = MediaPlayer.create(FlashLightActivity.this, R.raw.alert);
        mediaPlayer.setOnCompletionListener(new MediaPlayer.OnCompletionListener() {

            @Override
            public void onCompletion(MediaPlayer mp) {
                // TODO Auto-generated method stub
                mediaPlayer.release();
            }
        });
        mediaPlayer.start();
    }