When [William’s] thermostat died, he wanted an upgrade. He found a few off-the-shelf Internet enabled thermostats, but they were all very expensive. He knew he could build his own for a fract… ...

First off, they looked into a plug-in thermostat controller, and found a cheap one called the HeaterMate. Unfortunately it left a lot to be desired.

Four engineers from Spark have pooled their skills and resources to create a new open source smart thermostat based on Arduino using $70 of components.