I stay in a lot of hotels for work.  They all have credid card like
keys that electronically open your hotel room door.  I was told that
embedded in the card is all of the information you gave the hotel,
including your address, credit card numbers, and expiration dates. 
Someone with a card reader, or an employee of the hotel, can access
all that information with no problem whatsoever.

Is this true?  Or do they just open your door.  Please provide some
reference source to document your findings, thank you.