I Found this site, and it’s awesome. It’s how to hack your doorbell and get personal sound of who is your guest. It’s so easy, so I think everyone is able to hack their doorbell. But I’m not recommended this thing to who doesn’t like electronics.

Below is the parts that you can buy @ amazon.com
Find a doorbell here
Sandisk Sansa Express 1 GB MP3 Player
Find the speaker here.