Door Entry Announcer Project

I am new to arduino as well as this forum. I have completed some basic beginner projects and still dont really know what I am doing. LOL. I think I have learnt more from just tinkering around than anything. I have been asked to find a door entry buzzer for my parents small office but they dont want a wireless one which is pretty much everything I have found online. They basically want a door sensor with a wired speaker placed in another room to notify them if someone enters through the back door.

I thought this would make a good little project rather than buying one. Does anyone know if there is a follow-along project for something like this?
I'm sure it would be much cheaper to just buy one but I would much sooner learn how to make one if I could find a similar project to follow.

Edit: This circuit has a time delay, this may not be what you want.
You don't need a micro controller for something as simple as that. Here is a nice way to build an Alarm.