I know a lot of people out there have alarm systems they either inherited when they moved in, or just grew tired of paying the monthly fees. Wouldn't it be great to use the existing magnetic sensors, motion sensor, glass break sensors and perhaps even the keypads? I was thinking that setting up an IO monitor with the Raspberry Pi would be great. There would have to be an ability to arm and disarm the system and have alerts sent out via email and possibly others like SMS.