Locks and keys in Art Thief HD

I've been working on the lock and key system in Art Thief HD. How does the thief gain access through security doors?

There have been written a number of interesting articles on how to implement a good lock and key system. The example most often mention is the system used in Castlevania where each key doesn't open a single door but adds ability to the main character instead allowing him to reach places not available before.

Adding abilities to the thief would I think distract from the realism of the game so I've decided to use a key card mechanism instead, similar to the one used in Impossible Mission. Every guard in the museum has a key card with a code and every code activates or deactives certain security systems in the museum. For example one code could simply open security doors while another might activate certain elevators. The trick is that the codes have to be memorized as they have to be punched into a key panel located on some floors. I think adds to the educational value of the game. Part puzzle game, part memory card game.

I have also been looking at Shadow Complex, a highly impressive game for the XBox, and hope to emulate certain special effects from that game.