I have broken in to many houses through the garage door, because the car inside the garage was on fire.
It is not easy and not something that can be done easily without attracting a lot of attention (at least in Southern Nevada where most garages are the main feature of the front of the house). Long before I tried to pry open a garage door, I would kick in the door to the house.
Yes, you can pry the door from the bottom. I have done this. Once you get the pry bar under the door, you can break away the last section of the door.
The best way to get into a garage door is to cut a triangle in the door with a gasoline powered saw. Locks and C-Clamps won't prevent either method.
That thing about pulling the release cable from outside seems pretty challenging to me. Usually that cord is about six feet or so from the door. So, you would have to get the tool inside the door, then feel around with the tool blindly until you found the cord. Possibly, but tedius.
If we need to get into a house and have time to be careful, we check all the doors and windows to see if any are open. The majority of the time, they are: one window, the rear sliding glass door usually. If not, we try to open a window by tripping the lock from the outside using some kind of improvised tool depending on how the window is latched. Some people even carry lock picks (
But, if worse comes to worse we just break in. And, there is very little you can do to stop it. In the acedemy we spent an afternoon breaching sold steel reinforced concrete walls with a sledgehammer (while breahing air). Note that the equipment used is not some speical tool available only to certain people, anyone can get a sledge hammer and you can get into anything with a sledge hammer.
I see this garage door thing as being another one of these situations where, if someone wants to get in bad enough, they will. You can do whatever you want to the garage door and they can still break a window in the house, kick in a door, breach a wall, whatever. You are not going to keep them out easily. A standard garage door is pretty secure.
" Anything in the garage that is capable of cutting (power saws, etc) resides in the took cabinet"
I would be far more worried about things like sledge hammers and axes than power tools.