How can I make my web-based appointment application produce an audio alert when someone is late for the appointment?

Wouldn’t you have to tell what software you’re using for us to answer that?

You can play sounds using Javascript. Facebook Chat and Campfire are two applications that do this. It’s compatible with most browsers. This document explains how to do it.

If anyone is reading this and considering adding background music to their website, DON’T DO IT DON’T DO IT DON’T DO IT. Thanks.

If you don’t have access to the source code, there’s very little you can do to change the behavior of the application.

Oh wait, I misread. I thought you were involved in the development. Not particularly then, I’m afraid.