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Comment by Erazal | Hacker News Reader

Wow I'm amazed by the option of adding a chip from a tap to pay card.

This would be a lot better than an NFC chip on a standard smartwatch as the F91W could last for years with that chip inside it.

The F91W is cheap, and really reliable. I've always fantasized about modding one, and this exactly would be my dream. Sadly, I don't have enough time on my hands.

If it were for sale, I'd buy it immediately !

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Your wish is almost granted: https://n-o-d-e.shop

The link is at the bottom of the site, but it's pretty subtle, and I think these watches have the same mods.

Edit: These have NFC, but no SD card, so maybe they will show up with enhanced storage later, but anyone wanting the NFC features with the watch it looks like they are available.

Edit Edit: The NFC chip in the ones for sale is not tap-to-pay :( still neat though!

It is possible to scavenge the NFC antenna/chip from an Oyster card or indeed any other card, which the author alludes to in their video. There are details floating around on how to do it, by dissolving the card in acetone.

However, the relevant authorities might take a dim view of repurposing the transit card in this manner and probably have certain restrictions in place, to deter people from defacing their property. On another note, the author is using a NTAG213 on the watches sold via the shop and Oyster is Mifare, from what I can remember. There might be issues with response times regarding the proximity to the reader, if you wanted to experiment.

I follow someone on twitter who explained how to do this at one point, using a Caltrain Clipper card, and put it in a resin ring :)

I could dig that up if it’s helpful but in general I think it’s pretty straight forward, just some risk of destruction :)

Oh, thank you so much ! I'll guess I'll be adding another F91W to my collection :)

It says: "Be aware, this particular NFC chip is NOT compatible with tap-to-pay."

hum... That's sad. It's almost there ! Does tap-to-pay require specific maker certificates ?

Tap to pay requires you to extract the certificates & private keys of a real card. You can write (or license) an EMV applet for any JavaCard or similar smartcard that allows you to run arbitrary code, but without the keys associated with a valid payment card it won't do anything.

While it does seem useful, I’d be curious of the security implications; does wearing such a thing on your wrist make it easy for others to scan your credentials? I’m not incredibly familiar with NFC chips, but they do seem to have a much shorter range than most regular RFID chips, which seems like it might help. However all anyone would have to do is embed a reader under/in the table you sit at (say, at work or at your local coffee shop). Maybe we can keep the circuit hidden in a faraday cage, such as another (modded) microSD card slot, and just pop out the chip when needed.

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