Store your RFID transit card inside your cellphone

Check it out, this is a Boston transit pass — or at least the parts of it that matters. [Becky Stern] got rid of the rest in a bid to embed the RFID tag inside her cellphone.

The transit pass, called a CharlieCard, started out as a normal credit card shaped tag which you might use for access in the workplace. She unsheathed the chip and its antennae by giving it a generous soak in acetone. In about thirty minutes the plastic card looks more like paper pulp, and you can gently fish out the electronics. These are now small enough to fit in the back cover of a cellphone much like those inductive charging hacks.

[Becky] put hers in an iPhone. But the idea comes from [Dhani Sutanto] who used the same technique to extract the coil from a London transit pass. He then embedded the hardware in a resin cast ring.


  1. donnie darko says:

    I had done this with my rfid badge from work. Depending on the phone, you may have a harder time getting it to read. It won’t fail every time but when it does you end up having to yank the back off your phone. Same thing even if you put it between the phone and a rubber case. Not guaranteed to block the signal but if you have trouble getting it to read, that’s why.

  2. Jeff says:

    I have always wanted to do this with my work RF tag.

  3. skitchin says:

    Hypothetically, couldn’t you have also just put the whole card into your phone case?

    • gabe says:

      but then, how else she will have an excuse to smell all that volatile ammonia?

      If you want a decent hack, then use the NFC most phones already have, and program it to emulate the badge/metro card. …and glue a copy of the printing of the card on the back of the phone in case anyone asks.

      • Joe says:

        Exactly. I’ve been doing this. There is enough room inside my Galaxy’s case for my Charlie card. But chemicals and fumes are fun!

      • adcurtin says:

        Maybe you should watch the video first. They said the card as a whole wouldn’t fit in the back of the iPhone. Also, regarding using NFC, do you think these things don’t have security? Also, why do that when this is a lot easier?

        • I do not disagree with your logic. The problem is, hackaday readers don’t CARE if it’s easier. Most of us just want to hack it. Thank you for your human concern. Unfortunately, not just humans seem to use this site…

  4. 8complex says:

    Or you could get a phone with NFC and then hack the kernel to support emulation mode. This would broadcast the RFID string that you recorded from another card, basically cloning that card. You could easily have multiple cards on a single phone, without any chips at all.

  5. Jarina Roy says:

    If you are dependable on your cellphone, you should know about the RFID string that you recorded from another card, basically cloning that card.

  6. Steven says:

    Charley card?

    • dana says:

      “M.T.A.”; AKA “The MTA Song” or “Charley on the MTA”

    • dana says:

      I realize my previous comment wasn’t very informative.

      From Wikipedia:

      “The CharlieCard is a MIFARE-based, contactless, stored value smart card used for electronic ticketing as part of the Automated Fare Collection (AFC) system installed by the Massachusetts Bay Transportation Authority (MBTA) at its stations and on its vehicles.

      “The CharlieCard is named after the title character in the 1948 protest folk music song, “Charlie on the MTA”. The song was written to protest a fare increase in the form of an extra five cent exit fare for longer rides and was later made popular by the Kingston Trio in 1959.”

  7. draeath says:

    Keep in mind you shouldn’t be reforming the coil. It needs to keep that same diameter and number of winds, or you’re changing it’s characteristics as an antenna.

    • April says:

      We do this all the time with ham radio . Yagi and quad antennas are just dipoles folded or attached a different way . If you bend the wire back on itself it will affect it but as long as the length stays the same and its not bent back on itself the characteristics won’t change much. The pattern it emits will however if it transmits but power will mostly stay the same

  8. Steven says:

    Sorry, should have read before posting.

  9. Ren says:

    The acetone won’t dissolve the varnish on the antenna wire?

  10. Matt says:

    I did exactly the same with my RFID card at work. Luckily that was a two piece affair held together with glue. Judicial use of a hair dryer released the antenna and chip, and I used a craft knife to carefully excavate a recess into the back of the battery cover of my phone, and used a piece of sticky backed vinyl to seal it all in place. Job done. It always makes people do a double take when I swipe my phone to get into the building.

    One drawback however is that it makes it harder to take your card out with you on a lunchtime run. You dont want your phone banging about in your pocket. Thankfully as my tag is held in the battery cover, I can just detach the cover and take that with me.

  11. Hirudinea says:

    But if you lose your phone you can’t get home or call anyone to pick you up!

  12. mental2k says:

    Really cool hack. RFID really is like a little modern magic. I keep meaning to buy a reader to I can play around with it. Some day I suppose.

    In the mean time I resolve this problem by keeping my work card in my wallet. Though I’d rather hide it in my watch and have a little ATTiny acting as a key chain. It’s hard to justify though as I only actuall have 1 RFID card ;-(

  13. Comments says:

    Don’t leave it in the acetone to long! I left a RFID card overnight and EVERYTHING dissolved :/

  14. chris says:

    nice! now i have to get a job where RFID cards are required…

  15. tedmeyers says:

    Wait, Becky Stern works for Adafruit? I thought she worked at Make — shows how much I’ve been paying attention.

  16. Kevin says:

    Aren’t there any people doing ticket controls? what do they say when you’ve destroyed the card? Here in Sweden they walk around in the trains checking everybodys tickets quite often.

    • Dan says:

      When the ticket inspector comes along all they want is the data from the card to say you have paid. If the card is inside a wallet they can just scan the wallet.

      There is not benefit to them of looking at the front of the card as it has no information on it, unless it does like student etc.

      They might give a strange look if you offer them a phone to scan and may be worried if you have cloned the card. The defense is to say you just made the card translucent and light, but it’s still the same card.

  17. caramono says:

    sadly, I cannot do this. In the metro system here, you need to put your card inside a card slot to recharge.

    card-sized phone, anyone?

  18. Libs says:

    Why bother when we will use NFC tags… near field communix.

  19. Blue Footed Booby says:

    In college my dorm had an rfid reader on the front door. Not only did I not bother taking my ID card out of my wallet, I didn’t even take my wallet out of my pants. I’d just wave my butt at the sensor and the door would unlock. Half the people who saw me do this looked at me like I was insane. The other half said “wow, I didn’t realize that would work. :D”

  20. Jonathan Wilson says:

    This wouldn’t work for my transit system, firstly you need to insert the card into a slot to recharge and secondly the transit guards would probably fine me if they couldn’t inspect the card.
    Nice hack though if you can get away with it :)

  21. GotNoTime says:

    Don’t do this with the London Oyster card. TFL and the actual tube staff get annoyed with you if they catch you.

    Wikipedia says TFL may fine you but I just got told to get a replacement card which they gave me for free *shrug* The staff at the actual stations didn’t seem to care but a ticket inspector on the train itself didn’t appreciate it.

  22. gleen close says:

    I ended up sewing a flap of fabric to the front of my slacks that holds the card when not in use. I am also working on a multi-pocket leather carrying case for all of my various cards and even paper money! The future is here my friends. One of my friends tried to convince me to build a large pocket on a strap that was big enough to carry a book! I told him that was pure hilarity and I couldn’t imagine a world where people would carry such large things and walk on the moon :)

  23. Jim McCoy says:

    Breaking out the chemicals once I get home, my Charlie card has seen better days.

  24. Drittonns says:

    Hi guys, i just wanna know what kind of chip is on RFID Card cause i cant find what kind it iss.. ?

  25. Heinrich says:

    Hi Guys, im trying to find out which type of RFID card works with smartphones?? Can any one help

  26. Baso says:

    You need a smartphone with NFC. Then it can read NFC cards.

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