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Sometimes I forget my RFID door access card at home when I go to work, and when this happens I must stay in the building for the rest of the day or have a friend let me in if I leave during the day (i.e. to go to lunch).

My Galaxy S4 phone has NFC capability. Is it possible to record my RFID door access card to my phone so I can use my phone in lieu of my card for times when I forget my card?

I have not found any apps which will do this, so I am wondering if the phone is even capable of performing this function.

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  • I doubt it. Especially since there are several types of RFID implementations. MIFARE alone has several variants.
    – Oliver Salzburg
    Oct 2, 2013 at 11:45
  • @OliverSalzburg multiple applications exist in Google Play to read and write RFID cards. I would be surprised to learn the NFC functionality can read and write RFID but not play it back.
    – steampowered
    Oct 2, 2013 at 12:03
  • @steampowered - Have you tried those applications? There are so many things they could do to make the RFID difficult to clone.
    – Ramhound
    Oct 2, 2013 at 12:26

3 Answers 3

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Assuming the RFID system you are talking about only expects a key, and then does a look up in the user db.

Usually, a new UID is generated for each NFC transaction by phones. Some users have been able to maintain a static UID sent from the phone to the RFID receiver. A static UID will then act to send a constant "key" across to the RFID receiver instead of a generated one, everytime you try to swipe the device.

To obtain the static UID, you need to change the firmware on your phone, to only send one UID. Users on this forum have achieved it on the Google Nexus S and EVO 4g LTE.

Happy days!

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  • I was definitely assuming the state of the RFID card does not change from one swipe to another. Interesting - I never thought about the possibly that the RFID card was storing a token or some other data for the next swipe. I also never considered the phone changing the UID for each transaction. Interesting thread you posted - I will let you know the results of my tests tomorrow when I bring my card to work.
    – steampowered
    Oct 2, 2013 at 14:43
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You can melt the card with acetone, which will get you the chip and antenna. You could then stick them inside your phone cover and use it as an RFID card.

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    That's certainly a great idea if you have to return the card at some point and nothing is left of it.
    – slhck
    Jun 18, 2014 at 13:52
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    In that case I will tell them that I lost it.... $4 max.
    – A.D.
    Apr 1, 2016 at 15:41
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It depends on your access-control system. Normally, the UID of the card is not used in access control, but rather encrypted information on the card. Therefore, it is not possible to clone/record your RFID card.

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    There is a message being sent to the card reader. Assuming that message doesn't change, I should be able to play it back. Am I missing something?
    – steampowered
    Mar 12, 2015 at 3:28
  • 1. not only 1 message, there are protocolls for comunication between reader and card, depending on the card type.
    – ThomasK
    Mar 13, 2015 at 10:38
  • 2. for example if you have an mifare Desfire card, the relevant information (something like an access control number) is send encrypted to the reader. According to the protocol reader and card 'generate' an session key for encryption.
    – ThomasK
    Mar 13, 2015 at 10:45

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