Although this guide will provide most of the technical details to complete this project, there are a few things you'll have to do on your own.

So the first step is to take apart your garage door opener (the one mounted to your wall) and figure out how it works. There's a good chance that your garage door opener works in a way similar to mine.

I unmounted the opener from the wall and opened it up. There was a red and a white wire that were secured to the PCB (circuit board) by screws, so my first guess was that this operates like a normally open switch and if I connect the wires (and close the circuit) it will activate the garage door.

To test this theory, I hooked up my own NO (normally open) switch to the two terminals on the PCB and tested it out. To my delight, it worked!

So with this mystery solved, our circuit is going to be pretty straight forward. We'll put a relay in place of this switch, and the Raspberry Pi can drive that relay.