You'll need an Arduino along with a bunch of various sensors to get the project rolling, and once it's all set up you'll have a simple, but cheap system to monitor your home.

By the way, we’ve covered a PID library for Arduino before. While this post talks about temperature, PID control is used for everything from flight control to levitation.

There’s an Arduino with a custom shield that interfaces the barometric pressure sensor, real-time clock chip, a digital temperature sensor, and a humidity sensor.