If you have the keypad, I just use the same code from car to car. Since you can program your own.
I've had keypad entry in the folloiwng cars:
81 T-Bird
93 Bronco (installed from a Merc Sable as the Bronco didn't have it that year)
01 Explorer
05 Freestar
06 Monterey
15 Expedition
I just program the same code into the next car when I get it. I'm not even sure what actual factory code is on my current cars.
I will say that I rarely use it as much now that I have a working fob. But my fobs tend to fail after a few years even with battery changes. But the other day I did leave my keys in the ignition when I thought I had removed them. I locked the car up and walked off. I then felt up my pocket and knew they were missing. I went back to the truck, keypad'd my way in and there were the keys. If it hadn't been a keypad vehicle, I would have had to call the wife or AAA. I love the keypad and I'm surprised that Ford is the only it seems that still is using it.