Making Monster Objects Solid?

I'm trying to make a door object that disappears when the screen is triggered by interacting with another object. However, the door object is passable, and I'm not sure how to make it impassable. Is there a way to make the object impassable? Am I simply missing something obvious?

You could make a "All pickups lock" tile for your Door tile, put your door tile on a screen, and assign a "Screen Type" number in your Screen Info... (choose the number you want).
Then make a "key pickup" in game objects, and put it on a screen, and assign the same "Screen Type" number.
When the "pickup" is taken the screen (the ones with the same screen-type number) will be triggered and the door will disappear.

If you're looking for locked doors / keys sort of thing...that'll be in the first adventure game module in just a few days.

I'm looking to do so as well, but for completely different reasons - in my game I have these signposts player can interact with, but they're completely passable.