Do-It-Yourself Home Security?

pussycat asks: "Having recently purchased a home in an urban area, I am investigating monitored home security options -- I'll feel better when I'm away, and I'll get a break on my insurance. I am rejecting the big security services like Brinks because of their very high monitoring fees: $25-45+/month. I've found a cheap monitoring service (911Alarm has one for $13/month), but I'm overwhelmed by the choices for hardware. SmartHome has some nifty devices, but the hardwired stuff looks like a real pain to install, and the X10 stuff seems kind of cheesy. Does anyone have experience with setting up a do-it-yourself home security system? I'm interested in reliability (minimizing false alarms) and low-cost." Has anyone wired up their own home security system? What things should one watch out for when tackling a job like this?