UPDATE!!
30/05/2013
Had issues with the home made keypad so make this second front panel (Top Half V2) which takes the Numeric Keypad from Maplin (http://www.maplin.co.uk/numeric-press-button-keypad-220344). It interfaces with the alarm the same way. Also I had issues with the LED's which stood off of the PCB. They broke the tracks so I also moved them to the side of the box to be better seen through the shed door's window.

A friend of mine wanted to have an alarm on his shed/garage. He had brought one but it failed to work correctly after about a year.

He then asked me if I would be able to create him a simple little system to help protect his stuff. This is the result of that request.

It has two circuits, one for PIRs and another for door switches. Run by a 4 digit code to turn the alarm on and off, internal and external sounders/alarms.

In the picture the base of the case is two tone, this was due to me running out of filament through the print and inserting a new (different colour) filament while it was still printing. It is only meant to be printed one colour, no dualstruder needed!

The system is built around the Arduino. I had a rubber top from a keypad which I used for the pin entry. It needed a custom PCB to run (has those little conductive pads on the back of each key). It is wired up as a standard matrix keypad so can be replaced with a similar off the shelf keypad.

I have included the STLs for the case as well as a SketchUp file if you wanted to modify it to take a normal keypad. The circuit diagram is included as well as the PCB. The case has stand-offs for the PCB's that line up with the holes in the actual board. I used M3x6mm self-tapping screws to secure the PCBs to the case and the two halves of the case.

The case bottom has slots for attaching to a wall, but the holes where the heads of the screws go to attach the halves together will need to be reamed out.

The keypad attaches to the 6 pads to the left of the ATmega, top 3 columns, bottom 3 rows. It only uses 1-9 for number input as I originally planned to use a 9 button keypad that was made with keyboard switches. The Sketch can be altered to use the final row, although the PCB would need adjusting. I included a FTDI header using the layout Sparkfun use for their FTDI-USB cables.

I have included the instruction PDF I wrote for my friend which goes through wiring, connectors and LEDs.

Wasn't going to put this up, but someone might be able to use it or get inspiration from it.