It would actually be a bit easier than that. Check help door or redit-exits (same file)
For 20701 (you can see this is help redit-menu)
you're going to start with 5:
5) Exit north : -1
1) Exit to : -1
2) Description :-
<NONE>
3) Door name : <NONE>
4) Key : 0
5) Door flags : No door
6) Purge exit.
Enter choice, 0 to quit :
So, 1 is 20702. 2 is your choice, 3 is your choice. 4 is the key number. 5 is either 1 (pickable) or 2 (not pickable).
1) Exit to : 20702
2) Description :
/c
This door is locked.
/fi
/s (These / lines won't show. I have them here as a reminder)
3) Door name : door oak
4) Key : 207xx
5) Door flags : 2
6) Purge exit.
Enter choice, 0 to quit :
0
Now, from redit 20702, you choose 7:
7) Exit south : -1
1 will be 20701, 2 is your choice, 3 is your choice, leave 4 alone, 5 is 1.
1) Exit to : 20701
2) Description :
/c
This way out.
/fi
/s (These / lines won't show. I have them here as a reminder)
3) Door name : door oak
4) Key : 0
5) Door flags : 2
6) Purge exit.
Enter choice, 0 to quit :
0
Now comes the really fun part. Read help zedit-menu.
zedit 20701
N) New command.
What number in the list should the new command be? (probably 0 or 1)
D) Open/Close/Lock a Door
Is this command dependent on the success of the previous one? (y/n) N
This will not appear if there is no previous command.
0) Exit north.
2) Door locked
Quit and Yes
zedit 20702
N) New command.
What number in the list should the new command be? (probably 0 or 1)
D) Open/Close/Lock a Door
Is this command dependent on the success of the previous one? (y/n) N
This will not appear if there is no previous command.
2) Exit south.
1) Door closed
Quit and Yes
zreset and check to make sure the doors do what they're supposed to do. The door will now act like my kitchen door where I don't need a key to get out but it locks behind me anyway except that this door won't lock until reset or until locked manually with the key. You probably do want that 20702 reset in there though because, if you nohassle through the locked door, it looks messy to see the open door on the other side.
Another reason is that I don't understand the door physics here, as seen in my post:
www.tbamud.com/forum/3-building/3611-door-physics#4334
That said, I still think that it's a bug that closing a one-sided door will make the doorless side apparently impassable.
Okay, so maybe it's not so easy, but at least it's not a trigger
And it's good practice of redits, exits, and zedits.
Good luck.