From the department of good ideas:

A helpful commenter has a suggestion for BrickUnderground's perpetually locked out Rental Rookie: "I have a spare key hidden taped to the underside of a piece of decorative furniture in the hall on another floor in the building.  Periodically I go to check to make sure it's still there.  Nine years later it's still there and thankfully I only had to go for it once." Genius.