If you are looking for the a better way, global variables really isn't your answer, as DUTOIT said, I would go with a dictionary.
It isn't hard to understand at all, even if you never used it. A dictionary is a list with 2 colluns, imagine something like that
basically you can store anything on it, and if you check the value for banana for example, it will be 5.
Now back to your door, you can use only one instance of the door, create an instance variable on it ( I would go for something like "doorNumber"), so each door will have it's number.
Your dictionary would look like this:
The key part(left one) you would acess using "door"&Door.doorNumber. // Door would be the actual object, 0 means locked, 1 means unlocked (you can also use strings if you like, "locked"/"unlocked").
To check if the doors are locked or not, you can use:
Pick all "Door"> Dictionary, compare key> "door"&doorNumber, if equals 1(or "unlocked") set solid to false.
Let me know if I can help with something else(please tag me)