The “smart” power grid is all about making people aware of how much energy they consume–the problem is they quickly lose interest in acting on that information. If we really want to save money on heating and cooling our homes, the trick is to borrow a principle from good web design: never make the user think.

And what could be simpler than a home climate control system that, like the all-seeing eye of Sauron, knows where you are at every moment of the day, and adjusts the thermostat accordingly?

That’s what Hans Scharler, president of software at ioBridge, whipped together with a little Perl, an IO-204 board, Google Latitude, and the WeatherBug API. Scharler calls it Location Aware Home Automation.

Put simply, the system knows, via his smartphone, where he is at all times. When it becomes apparent, via Google Latitude, that he’s heading home, it springs into action.

First the system uses WeatherBug to look up the current outside temperature near his house in order to determine whether or not it should crank the AC or the heat. Then his Perl script signals his IO-204 board, which is connected to his home thermostat. (The IO-204, which I’ve covered before, is a favorite of hackers and a mainstay of the nascent effort to create the Internet of Things.)

What’s elegant about this setup is its simplicity–other home automation systems rely on burglar-alarm style sensors to determine when you’re home, but they have no idea how to predict the future or that you’re on your way home. Sure, you can set a timer, but what if work runs late, or you come home early, or you have an erratic schedule, or you’re on vacation? Who wants one more dumb machine routine to have to remember to reset every time your life circumstances change?

By using only a single specialized piece of hardware, Scharler has created a system that taps into existing infrastructure, including cell networks, the Internet, and an endless array of web-based services and APIs. If your phone knows where you are, why build a redundant system to determine that? And if your phone is connected to the web, why build a second, also redundant system to convey that information to your thermostat?

Scharler proposes this system as a way to make his house comfortable before he arrives home, which presumes that he’s set it up so that when he leaves, the climate control switches off. This is perfectly fine if you live in a relatively dry climate and you don’t have indoor pets–houses don’t need climate control when they’re not inhabited. Imagine if every home in the U.S. stopped pumping juice into its biggest energy hog–the HVAC system–every time its owners left. The savings would be staggering.

Scharler has made all of the code he used to accomplish this feat available on his website.