Thomas W. Lewis produced two excellent projects to remotely control his HVAC system and monitor his home power usage.
He wanted to turn off his HVAC system completely before leaving for an extended period of time, like going on vacation, and then turn it back on just before he gets to his house. Thomas found the controls wires on the thermostat and uses a relay to turn on or off the thermostat. He made it remote controllable with the ioBridge IO-204 module and control widgets placed on a mobile phone.
In additional to remotely being able to shut down his HVAC system, Thomas also monitors his temperature and whole house power using the analog inputs of the IO-204. He used AC clamps around the house power mains to get a power utilization relative to the current through the wires.
More details and photos are available on Thomas’ Smart Grid section of his blog.