Why are you a thief?
Wow that's a pretty outrageous claim, but yeah thanks for the support...
Any decent door opener should change the code every time making it almost impossible to crack.
They almost all do this, I'm not sure the protocol but I'd imagine some sort of token authentication. I also know it's possible to program a new device to the garage door, for instance my Infiniti I can program to open my garage door. I don't mind having to use the method Infiniti does and have your original opener there to program with, I'm essentially trying to design a garage door opener that is embedded in vehicles that otherwise don't have them built in.
Here's a car that can do this, and a demo on how to use it. I'm trying to accomplish the exact same thing that comes standard on millions of cars worldwide... Also note that most garage doors have to register the devices which are allowed to open, which usually involves hitting an authorize button on the door then pressing the button in the car again. This is fine.