enclosed door bell

例句：

1. 1. The new security system has a built-in enclosed door bell to alert the homeowner when someone is at the door.
   新安全系统内置了门铃，当有人敲门时会提醒房主。
2. 2.The elderly couple installed an enclosed door bell in their home to prevent unwanted visitors.
   这对老年夫妇在他们家安装了门铃，以防止不请自来的访客。
3. 3.The enclosed door bell was a lifesaver for the elderly couple who had trouble hearing.
   这对老年夫妇的听力问题得到了这个门铃的帮助。