Making a Wearable NFC Bus Pass

[Stephen Cognetta] is trying to get the total number of things he owns down below 115, and he’s always looking for ways to streamline his life.

Toward this goal he dissolved his SF Transit Clipper Card in acetone to get at the NFC tag embedded inside. The tag consists of a tiny chip attached to an antenna the size of the card itself. It took about three days (video below the break) for the layers to separate and [Stephen] was able to extricate the tag.

He ended up trying a few different ways of storing the delicate chip and antenna, including a lump of Sugru as well as a waterproof aspirin band, pictured to the right.

One supposes the transit pass idea might save you a little time, but what would really simplify your life would be having a single wearable tag that unlocked a bunch of things. Also it should be noted that, un-coolly, damaging a card violates SF Transit’s terms of service…

HaD has covered NFC wearables before, including the phone-unlocking NFC ring as well as the NFC ring box. This NFC-controlled infinity mirror makes great use of the technology.

36 thoughts on “Making a Wearable NFC Bus Pass

    1. It will soften it a bit, but won’t really dissolve it (assuming it’s polyimide). At work I believe we use xylene to dissolve polyimide, but usually you just burn it off in a lye pot or something if you actually want to remove it.

  1. Speaking of NFC devices I’ve been trying to find info on reading car key transponders but not really coming up with any useable information. What information I have found is some what contradictory and lacking any technical detail.

    I could see the SF transit people getting a little upset by the modification of the card but it would be good for them to allow altering the form to suit personal use.

    1. Yeah. There should be a law stating “You shall not make unnecessary rules”.

      For it to carry some weight there should be some payment to the “victims” of unnecessary ruling (proving a rule “necessary” resp. “unnecessary” will be somewhat involved too, but the burden should be more on those imposing the rules than on those challenging them).

      The devil is in the details, of course. But you get the idea.

    2. The problem is they chose a crappy form factor the card. If they chose a capsule based NFC tag as an option then people would have been able to put it in their watch band or whatever, heck the keyfob is even better. I did that back in the days when Mobil gas had a NFC pay system, I took the capsule out of their keyfob and put it in my watch band.

      1. @timgray1 – I was just thinking of those! They actually did have a few watches (Casio, I believe) made with the NFC capsule built in to the watchband. I actually owned one, since I did work for ExxonMobil for the initial SpeedPass rollout. The “leather” watchband deteriorated quickly and the NFC capsule popped out, but was still a neat thing (hipster mode on) way back before it NFC/RFID was “cool”. :-)

      2. Chicago’s CTA has NFC transit cards too, but you add money to the card, so e-pickpocketing becomes a concern. In fact, Chase dished out NFC debit cards, and when both cards were in a wallet then used, BOTH cards got bilked out of the fare! I have one of these CTA “Ventra” cards and I taped 2 pieces of sheet metal to it like a butterfly knife. I also have, kept separate, an NFC debit card that I also protect with a sheet metal and tape pouch.

        Chicago had a forerunner NFC card 10 years ago when I discovered the problem. A lady boarded a bus, used her card, put it back in her purse, and when her purse rubbed against the reader, BEEP BEEP! she got zapped for another fare. That night, I went to a Home Depot, and protected the card a decade before the rise of the e-pickpocketer.

    3. > I’ve been trying to find info on reading car key transponders but not really coming up with any usable information.

      There is lots of similar standards and system. You should first work out what your own vehicle is using and attempt to read and clone it. Generally automakers use various third parties systems. Typically there is a remote control central locking on 433Mhz EU or 315Mhz USA. Then when you insert the key in the ignition barrel it uses an RFID non powered transponder that has a single ID with a number of bits. This is normally 125Khz EU & 134Khz USA. If the vehicle likes the unique ID it allows the vehicle to start when the key is turned. Often locksmiths can read the ID and put the same ID into a blank chip in another key thus cloning the ID, without needing to connect into the car and add a new ID to the system. Sometimes if you own two valid keys for a vehicle it will allow an unknown third key to be added. If you search for a particular make and model you may find spare keys, transponder, remote central locking guides and instructional videos on youtube. I managed to add an extra key to my vehicle. Another quick cheat is to remove a valid transponder from a working key, and glue it beside the reader in the ignition barrel. Then any key turning the ignition will see a valid chip and the car will start. You lose the security benefits, but you can get copied mechanical keys for a few dollars.

      1. If the chips could be easily cloned then why wouldn’t they do that to replace a lost or stolen key? Specifically for Honda and Nissan autos, when you replace a key you have to have all other keys present and the car is reprogrammed to recognize the keys. If you don’t bring one of the keys with you then it stops functioning.

    4. It’s probably because most attempts at cloning or ‘borrowing’ another tag at a distance etc would show a doctored card or an RFID device connected to an arduino etc
      So mandating the pass is the standard size/shape is probably going after the low hanging fruit of fraud?

    1. I have this problem with acetone when I make ABS slurry and I can’t seem to find a vessel, baring the container it comes in, that will seal tightly enough to keep it from evaporating.

  2. For the transit networks I have used here in Australia, not only would there likely be rules against damaging the card in this way but if the ticket inspectors decided to do a ticket check, you would probably be hit with a huge fine (since they likely wont believe that your funky wristband is actually a valid Go Card or whatever)

      1. Our transit system is like that too, I don’t understand why they won’t just let you use your phone. We have a network of car chargers called ChargePoint that works off of RFID tags or you can just install the App on your phone and use it straight away. It’s brilliant because I can leave the tag in the car glove box for anyone who borrows the car but then I don’t have to go fishing it out if I need to top up the car. It all comes out of the same account.

        1. Somewhere in Sydney they are trialing the credit cards PayPass system to let you do a ‘pre-withdrawal-credit-check-thingy’ when you tap on and finalize payment when you tap off.
          This would allow you to use your phone or watch’s payment process.

          Stupid idea. They should be selling personalized tags/wristbands/keyfobs/stickers etc.

          Haven’t given any thought to how ticket inspectors will check this but I’d assume this system would require a central database (shudder) of card numbers and payment details that they verify your card with.

          1. They’d just route the transactions to your bank the same as any other Visa or Mastercard transaction.

            So the ‘Centralised database’ of card numbers is your bank.

      2. Do NOT duplicate them. They are dodgy Mifare Classics, but copying them is breaking crypto laws and you can get in /serious/ trouble.
        Dissolving the card(50/50 acetone and xylene works great) and using the chip in another formfactor(I recommend also leaving the ‘Go’ part of the card so it looks right:) is just vandalising the card. $300 fine.. Instead of jail time.
        I did that to one of my spare cards and made a keyfob(Using a cheap keyring NFC tag) and most of the time the ticket inspectors don’t care so long as you tap on and it’s a valid card.
        Once or twice I’ve gotten a ‘we’ll only let you off this once’ or a ‘you really should get a new card’. “Just cut it up and glued it in.” works for half the inspectors. Others you need to explain what you did and why.

    1. My nephew in london told me a story – someone was seen using a magic wand to touch on and off on the london underground. Turns out this person had removed the chip from the travel card/oyster card, and glued it to the tip of a Harry Potter souvenir wand. No mention of robes or funny pointed hats.

  3. I’m not sure whether it’s a shame NFC cards are kinda hard to emulate or not. I’ve got a key card for the office that I’m always forgetting and at the same time I’ve stopped carrying my bank cards since my phone can fill the role, so I’ve been trying to figure out how to get my phone to act as a key card for the door. Unfortunately it can’t even get a successful read on the card as it doesn’t support… whatever’s at the heart of it.

    I’m sure there are security reasons why this is hard but convenience darnit!

    1. There are a number of different NFC standards and RFID is just a subset of them. Your phone only works with RFID.

      It’s a shame there’s no way for your phone to emulate an RFID tag but from a usability perspective, you’d need to open an App and choose which RFID tag to emulate before you touch it.

    2. There is little to no security on most RFID systems and any with even basic security are generally 20 year old crypto which is broken now.

      Ideally find out the make and model of the system in use an research this. Also using a good radio scanner check if it is 13.56Mhz or 125Khz, by putting it close to the reader on the door. That narrows down the systems in use. Generally unrooted phones dont allow raw access to the 13.56Mhz hardware, if the phone has this. Typically you need a system compatible with the standard in use, and then you can often read and clone the card. In some systems the card will not respond unless it sees the correct system ID, which is broadcast from every door.

      1. I should be more precise, my Android phone notices there’s a card nearby, attempts to read but fails to do so. I was using NFC Tag Cloner which reports “Low level read of this tag type is not supported yet”. I should really go ask the in-building makerspace people what’s going on, they recently ran a small competition and got entrants by having people scan their cards at an arduino or similar with an add-on board, they probably know more about what’s going on.

    1. He’d have 112 if he hadn’t had to own acetone, sugary, and a spare wristband.

      If you want to ‘simplify’, I own 2 things: a house and a car. Small stuff inside them counts as part of the larger item.

  4. 50/50 acetone and xylene works great and does it in about 2-3 hours. :)
    Doesn’t damage the chip at all. Some cards use printed/foil tracks so they just fall apart.
    Get a NFC tag/strap/etc of the form factor you like and transplant the chip.

    1. OK, duckducked it(eff google), an aspirin band is a red silicone wrist band(Lance Armstrong style) with water resistant chambers for two Bayer 325mg emergency aspirin pills for use when chest pan is felt. Cool idea itself!

    1. The card is most likely Mifare DESFire EV1. Assuming you are familiar with all of the necessary commands you only need to know the application ID, Algorithm, file ID, write and read key.

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