One of the things I’ve noticed about home security systems is how expensive they are! The monetization model for home security is to not worry about making money on the hardware but sell the monitoring service at high rates. This is needed to support call centers for monitoring all the devices on a 24×7 basis. I’d love to have an alarm system, but they’re prohibitively expensive. We Makers can certainly do better!
The goal of the system is to detect doors or windows opening. If you don’t expect the door or window to open, you know something is up. This tutorial only talks about the door/window sensors and the alarm sequence. There are all kinds of things you can add to this alarm system once you have it constructed: smoke/fire sensors, carbon monoxide detectors, and security cameras, to name a few.