Actually, it would be more like have the door card latch system programmed to use the loyalty card to open your door, as long as you stay there. When you check in the clerk scans your card in the system, when you check out, they delete it.

I think the existing system is not networked. Rather, they are all self-contained, but with some interchangeability.

Seems you would either need loyalty cards that can function like the key cards in the existing system, or a new system controllable directly from the reception desk.

I'd argue for smart cards, or at least something more secure than regular magstripe cards.

The reason this would not be beneficial for hotels is that a lot of them generate extra revenue by using the keycards as advertising space for local businesses.

If I'm not wrong they both vary in size. The door key card is a bit narrower than the rewards card.

Magstripe cards of that sort are standard sized, but I have seen keyfob shaped magstripe cards used for retail reward systems, used in manual slide swipe readers.

First the cards are programed with the doors you have access to which is usually just your room and outside entry doors unless you are an employee and the date it is good till. Next the hotels I have done work in do not throw away the key but re-use them. I was thinking of trying to make a card coppier using a couple read heads and a type of amplifier. Swipe both cards and the signal from one head would be written to the other. I know it's not that simple as there are timing pulses and stuff.B