Why my S3 device sounds when magnetic card is put on its back? Possible Duplicate:
  Why does my Galaxy S3 make a noise when I put it down?  




Why my samsung S3 play a sound when I put above my gym magnetic card? Only with this card the device play this type of sound. Nothing happen if I put it above credit card or other magnetic/chip support.
The gym card open doors and let me enter inside the gym if I've paid. There's a way (maybe an app) to read what happen when my s3 grab that card?
Your S3 has an NFC chip in it that can read and write NFC tags which are a type of RFID. RFID is most commonly used for things like identification chips for dogs and NFC for public transport payment cards like Octopus or Oyster. It's also in quite a lot of credit and debit cards now too.

The card will have some kind of tag in it - the NXP TagInfo app will give you information about what kind of tag it is.