My wife was always concerned that she didn't close the garage door when she left the house so I built a solution. I got a RaspberryPi, a breadboard and hooked a magnetic switch up to the the shuttle part of the garage door. That way the Pi can test if the door is up or down. Also, I hooked it into the posts on the garage door head which can send a signal just like I was pushing the button on the garage door opener remote. A little Python script with an embedded web server runs the whole thing. Now I can use my smartphone to check to see if the door is up or down and optionally open or close it accordingly. Works great.