Some interesting thoughts there. The YouTube video @dave.b linked does give a potential answer, in the section where it talks about the potential for readers to write to the card.
Some more facts, I checked a bunch of cards I had over the last two years against the projector to view the insides without destroying them.
The old prepaid card, pictured above, has the exact same circuitry inside as the card I received with my current account earlier this year, no difference there.
Looking at the Monzo card from the back reveals there is a lot of the circuitry going out of the chip, so I don’t believe it’s just there as a dummy.
All my other brand cards that support contactless only have one ring around the outer edge, and some times smaller circuits crossing the middle of the card, nothing anywhere near as complex as the Monzo cards.
I have also got a joint account once they released it, and I noticed the chip from the front looks different, it doesn’t have the extra metal around it, making it fairly small and compact, same look as the AmEx above. I thought it may be worth taking a look at this one too, and it turns out it’s also very different from the standard monzo cards.
If anyone can comment if they received a monzo card within the last two months, how does the chip look?
Anyways, back to that joint account card, whilst unfortunately I can’t show a picture, as it’s an active card, I have taken a good look, it appears that instead of a few lines going out of the chip from small to big like in the normal card, the joint card has six circuits, all slightly thinner then the normal card, and they all span the full length of the card from side to side, and join back with the main ring around the card, and no big black square at the top, instead it has, I counted, 12 very small squares in a sequence, all strung together by a circuit, right under the signature field. I can’t comment on how they connect back to the main chip, or if they do, as the lines get obscured when looking at them because of the mag stripe right above.
I presume MasterCard won’t be very keen to providing any form of full diagram of the internals of the card, if perhaps someone at Monzo can share what they’re allowed to, I’d be very interested.