[superuser2]

My favorite attack on hotel security is much simpler: the front desk will willingly print you a key for any room.

Hold out your keycard and ask for a duplicate. Do they take your card and swipe it? No. They ask for your room number, type it into the magstripe machine, and print you a key for whatever room number you just gave.

No electronics, skill, or even malicious intent necessary (you just "forgot" your actual room number). Look and act like you belong, and make a run-of-the-mill request. Discovered this by accident when I was ~12 and wanted to go to the pool by myself. Never actually tried to get a card for another room, but never had the desk actually verify my rights to the room when requesting an extra keycard either.

[cafard]

Maybe if you're 12. This spring I had to present my ID to get a replacement for a dead key in Philadelphia.

[superuser2]

No it still works. I mostly travel in the Midwest, though, so maybe security standards are just a little lower in Lawrence, KS than the big cities.