Jon - I always ask (or are given) at least 2
Elevator - yes, I first learned about this growing problem at a Hilton about 2 years ago.... I would think it would be the magnets in the headphones, but someone said it was the batteries in the chargers/case? Not sure I understand that.... but when I was discussing the topic with them (and they gave me a nice service recovery points bonus for complaining) they said the tech is old, the readers in the doors get dirty very easily and are flaky but the cost to modernize is - shockingly - too much.....

I just bought one of those MagSafe cases for the back of my iPhone - I wonder (assume so) if that will also trash the cards.....