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Some keycards are even completely disposable (paper / cardboard), though most of them are reprogrammable (plastic). I've seen hotel personnel swipe the card to grant me access to my room (with a new and/or unique key, etc.)

Definitely. I was more thinking about cloning the card so I could just use my phone to unlock the door instead, rather than trying to use it at some future date.

Often, the lock reads a time stamp from the keys and the lock only opens for fresh keys.