Steve already had a pretty smart thermostat running his house, but he wanted more control. After shopping around at some of the newer wifi thermostats he decided they still didn’t provide the level of control he wanted. So rather than buying one he decided to hack the one he had. His thermostat already had some wireless control so it was up to him to figure out how it communicates and control it himself.
By using one of those cheapo 433mhz wireless boards you see everywhere, and a home brew soundcard logic analyzer he was able to capture the broadcasts as an audio signal. Once decoded he used the arduino and a 433mhz transmitter to simulate the messages he had captured. Now his PC can control when the system is on and off on a very algorithmic schedule / and or make use of other sensors.