If you want to build simple and reliable burglar alarm system from few electronic parts try this – PIC based four channel alarm system. It monitors 4 normally connected (NC) input channels. If at least one of the channels loop is disrupted it triggers alarm and shows Activated zone by flashing one of LEDs.
Project is really well documented. Because project was developed as final project for Electronics coursework, it has more that documentation – it also includes deep analysis of each part of circuit. So material should also serve as nice tutorial for PIC starters. Or you can just simply build the project, grab source code and flash it.