First off, I had no idea this many people habitually worried about the state of their garage doors. I don't know how people manage without an amateur knowledge of electronics, programming and Linux administration. They must turn around a billion times before driving to the airport.
I wanted to better understand GPIO development while feeding my neurosis, so I decided to pair a Raspberry Pi with a Chamberlain universal garage door opener. The goal was to keep component count and cost low, remove any need for root access and re-use stuff I had laying around.
Instead of using relays on a wired installation, I was able to simulate a button press on the remote using a MOSFET. After tearing off the outer casing, I pried off the button and re-soldered on some pins of my own. A MOSFET and a pull-down resistor bridged the former button's circuit when the gate received a high voltage from a GPIO pin.
After the remote was wired up, I found a cheap webcam and installed http://www.lavrsen.dk/foswiki/bin/view/Motion for the security feed and motion detection. Motion has been a fantastic project to work with. The motion capture parameters are very tweakable, which helps avoid false positives for alerts and reduce storage needed for footage. The HP HD-3110 webcam I used worked out-of-the box with the Pi, so no hardware issues to speak of.
Once the distro was tightened up, the webapp was written and the remote was wired up I took an old WD My Book and use the shell as an enclosure for the whole thing. Any metal backplates had to be removed otherwise the wireless signal completely died; but otherwise some double-sided tape made everything a great fit.
So far the entire thing works well - security cam lets me know the state of the garage, and the GPIO pins let me trigger the garage door to open/close, all without wiring anything into the opener itself. Total build cost is around $108 and 12 hours of work, but by re-using stuff I had around the actual hardware cost was closer to $70.
A more detailed write-up is available at http://deckerego.blogspot.com/search/la ... age%20door