Man, I hate people with mindsets like that.. Which, unfourtenately, leaves me hating a scary number of people. I mean, I NEED to know how stuff works! Even if I might never use the knowledge for anything usefull I still love just knowing and the more one knows, the easier it gets to understand something new. Imagine where we as a species would be if everyone had that kind of mindset...
If that is your goal, go freaggin' do it! Your garage door probably has an open/close button on the inside. Hook up a transistor, relay, opto-isolator, whatever you like (or rather, need) to that. Add a switch that gets pressed when the door is closed and 2 thermistors. The ones they have at Sparkfun seem good, and Sparkfun showing you how to convert the readings into degrees is an added bonus.
So part count for something really cool this far:
- Arduino
- wires
- transistor (and relay, if the voltage is above something a transistor can handle)
- 2xthermistor
- button
What are you waiting for, man? Any tinker with some self respect has a switch and some wire lying around. Go out and hook it up to your garage door and make a password protected webinterface for it! (I can help with the web-stuff if you need it :))
Yeah, I know about X10. There is even an Arduino library for controlling X10 devices, though I don't know what kind of hardware I'd need to send signals from the Arduino to the devices. Would be a pretty smooth solution if a bit pricey. There are even dimmers, and every device comes in versions that can tell the central control unit their state. But then, why not just buy a starter pack that contains the "computer signal to mains wireing signal"-device and use that instead of the Arduino? =P