Do you have any child proofing devices on your front door?

My 2 year old just figured it how to open the door to our condo. Luckily it only leads to a hall way that has heavy doors to the stairs that lead out of the building, but obviously we don't want her wandering the hall. We could put a doorknob cover on but that seems like a fire hazard. She is still in a crib now and hasn't tried to escape, and there is a baby gate I can use when I'm leaving her unattended (like if I'm taking a shower), so for now I'm not worried, more just curious how others have handled it. We don't have a dead bolt at this point but could install one I guess.