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Step 11: Miscellaneous Final Points/FAQ

Won't hackers steal my credit card?

This is a very common question I get, that I tend to break down into a few parts. The first is that (AFAIK) with the new generation of RFID cards, the only current feasible attack is one in which you need to have a reader near the ring that's relaying the wireless data to a repeater that's near a point of sale terminal. Not impossible, but from what I know (and that brings me to my second point...)

Due to the difficulty, the fact that their reader would have to be within an inch of the ring, and the ease of skimming magnetic strips at gas stations or buying CC numbers by the hundreds off insecure website hacks, most people just don't bother with the first route. It's the same as when people ask me about my RFID car door reader that unlocks my car. "Couldn't they skim your chip and replay it?" Well yes they could, for a few hundred in equipment and a fair bit of time, or they could pick up a brick off the sidewalk for free and break the windows and achieve the same result. Honestly, I'm a lot more worried about the second one.

Will this work for other RFID/NFC/whatever chips?

Definitely. As long as you can get the main chip down to a width of less than your ring width, then you're good. I'd also be happy to modify the models a big if you're trying to fit a bigger chip in, feel free to contact me. What I found is that since the antenna is acting as both an inductor and an antenna, you generally want the fewest loops, but also want to keep the length of the antenna multiples of the original antenna's length.

For other RFID chips I would say measure the overall antenna length, then wind one made of magnet wire that's double that length, one that's the same length, and one that's half that length. Since most of us don't own antenna analyzers (Or am I the only one that's not a cool kid?) you can just test real-world range on a reader with those three and you'll very quickly find out what works.

I tried the original antenna size wound around the ring and found it worked, but you had to press the ring right up against the reader. I also tried 1/4 size and same thing. Half of the original 30 inches and you don't have to talk the ring off your finger to use it. It's a balancing act between picking up power and relaying back the data RF packets. You'll probably find similar results no matter what you're starting with. If your original antenna length is very short, you might even try 4x when you wind the new one on your ring, just to see if it works better.

Is a ring the only form factor this will work for? Can I make a bracelet or something like that the same way?

Absolutely! The best way to figure out if it will work is just to try.

The good news is that the larger you go, the longer the range should be, although that falls off at some distance (A few inches.) no matter what. I'd be curious if you could bend your wrist enough to have a bracelet work at a point of sale terminal without having to take off the bracelet.

The other good news, is that with a larger form factor, there's more room to work. For a bracelet what I would do is start by taking out the chip as outlined in the instructable, then looping it to about the size that it would be looped for on your wrist. You can easily solder new length antennas on to test, and just trying it is definitely the best way I've found to see if it works.

There's talk in the comments of magnet wire that will strip itself when soldered, and that's definitely going to be the easiest option for testing. Let me know what you find out, sounds like an awesome project!

Super long/single loops like you'd have to have for a necklace would not work very well. You need a few loops for the inductive properties to work, although you might be able to take off the necklace and loop it back on itself and have it work. A bracelet should work well, although you may find out you have to take it off. Max range no matter what will probably end up being about two inches.

AxelFoley772 months ago
Pretty Impressive
Asmodeo4 months ago
Gorgeous! I'll try with the public transportation card !