So I picked up an Arduino. Its' a board with an ATMega328 microchip and some other cool s**t. It has 14 digital input/output pins (of which 6 can be used as PWM outputs), 6 analog inputs (which can also be used as digital outputs), and a 16 MHz crystal oscillator. You can do all kinds of cool things with it like control a UAV, make a security system, or almost anything else imaginable.
There are stackable 'shields' that you can buy for it which add on extra hardware like ethernet, wifi, bluetooth, etc.. I bought the ethernet shield so I could communicate with it over the internet.
The plan for now is to have it monitor all doors/windows in the house as well as have a few PIR (passive infrared) motion detectors in/outside the house. When the system is armed and a sensor is tripped it will sound an alarm as well as notify me via phone/internet. I might add in a bluetooth module so I can disarm it without entering a code. I'll also be able to open/close the garage door and lock/unlock doors from my cellphone or a web page.
Once this project is done I'm going to wire another one of these up to my xbox 360 controller to convert USB keyboard/mouse input into xbox 360 controller output. So I can own people on Call of Duty 4. I think I could kick some serious a** if I was using a keyboard/mouse instead of a controller.
Magnetic reed switches I picked up from eBay:









