How do hotel room key cards work?

I was told that my card would expire at normal checkout time and they had to recode it to allow me a late checkout. Since it is only magnetic info on the card that can't ';expire';, how does the lock know to keep me out if I don't recode the card? They didn't do anything to the lock, so what are they doing to the card to let it work for 1 more hour?How do hotel room key cards work?
All the hotel room locks are wired back to a central computer in the hotel. When they issue you a key card, they run it through a magnetic wirter that puts certain data on the stripe. When you insert the card into the lock, the lock sends the info back to the computer, which then tells to lock to unloack and let you in.





If you never turn your card back in, say you just drop it in a trash can, someone else could pick it up and get into the room. That's why the code on the card is only good until checkout. If you stay longer, they can change the code in the computer, but your card needs to be updated with that new code. Just like magnetic tape, the stripe can be written, and rewritten, to it.How do hotel room key cards work?
I don't think they ';re-coded'; your card as they said, but just gave you a new card with a new access code. Their system is set up so that any change in check-in/check-out status generates a new ';lock'; or access code (which keeps former guests from using their old cards and coming into your room).





It's not the information on the key/card that expires but the information on the lock.
My son does Mar-lock systems as part of his job. When I see him tonight (I live with him) I can get this info for you.