How do those hotel card keys work? I know that they get "programmed" for your door at the front desk, but how? The door's lock doesn't seem to be hooked up to a network of any sort. Does each door have one "combination" and the card you are given is coded to unlock it and then set to expire at the end of your stay? The doors have a red and green light that indicate if the card key worked, are these lights battery powered? I was looking closely at one yesterday and could not find anyway to get into the thing... No screws, no removable face plates, nothing... How would they change the battery? Do the maids get a card key that grants access to all the rooms... I am trying to find a way to keep my mind engaged while on business travel... Excuse the insipidness... ducks