Products claiming to be card-sized usually aren't actually card-sized
In the long human tradition of asking how small a thing can become before it ceases to be itself, a maker named Krauseler has answered a quiet engineering question: a fully functional computer — processor, display, wireless communication — can now live inside a wallet, indistinguishable from the cards already there. Built not from commercial necessity but from the frustration of seeing the promise of miniaturization perpetually deferred, this credit card-sized device invites the world to decide what such a thing is actually for. It is a reminder that invention and purpose do not always arrive together.
- Existing 'card-sized' gadgets have long bent the definition — Krauseler built something that finally keeps the promise, matching a credit card in every physical dimension.
- Packing an ESP32-C3 processor, e-ink display, and NFC chip into that footprint required constraint-based engineering where every millimeter carried consequences.
- The open-source schematics are already on GitHub, making the design reproducible — but the creator is openly asking the community what this device should actually become.
- Proposed uses range from wallet-resident smart home dashboards to two-factor authentication tokens and NFC pass storage, each solving a small friction in daily life.
- The honest tension at the heart of the project: the technology is proven and the form factor works, but the killer application has not yet declared itself.
There is a particular kind of maker who looks at the space inside a wallet and sees an unsolved problem. Krauseler is one of them — and they have built a working computer that fits inside a credit card not in spirit, but in fact: same dimensions, same thickness, the kind of object that could slip between your license and insurance card without anyone noticing.
The frustration that drove the project was specific. Products marketed as 'credit-card sized' have long cheated the definition, arriving slightly too thick or too wide to truly earn the label. Krauseler wanted to build something that felt like a credit card in your hand — not a novelty, not an approximation, but the real thing. The result packs an ESP32-C3 processor, an e-ink display, and an NFC chip into that impossibly constrained footprint.
The appeal of the project is partly the engineering challenge itself — brutal space limits force different thinking, and every component choice cascades into consequences. But there is also something more elemental: the fantasy of genuine computing power living quietly in your wallet, without the bulk of a phone or smartwatch.
Krauseler has published the full schematics on GitHub and has thought through potential applications — a smart home status display you can show without reaching for your phone, a two-factor authentication token that lives where your cards already live, a digital holder for transit passes and event credentials. Each idea has a certain elegance.
The refreshing honesty of the project is this: Krauseler built it because the constraint was interesting, because the question was worth answering. Purpose came second. Now that the device exists, they are asking the community what it should do — an acknowledgment that sometimes the invention arrives before the world knows it was waiting for one.
There's a particular kind of maker who looks at the space inside a wallet and sees a problem to solve. Krauseler is one of them. They've built a working computer that fits inside a credit card—not a card-shaped computer that's slightly thicker than a credit card, but an actual credit card: the same dimensions, the same thickness, the kind of thing you could slip between your driver's license and your insurance card without anyone noticing.
The device packs an ESP32-C3 processor, an e-ink display, and an NFC chip into that impossibly small footprint. It's a genuine feat of constraint-based engineering. The motivation, according to Krauseler's documentation, came from frustration with existing products that market themselves as "credit-card sized" while still feeling like they're cheating the definition. AirTag-style trackers and similar gadgets claim the form factor but don't quite deliver on it. Krauseler wanted to build something that actually felt like a credit card in your hand—not a novelty, not a prototype that's "almost" the right size, but the real thing.
The appeal of extreme miniaturization is partly about the engineering challenge itself. Making something work within brutal space constraints forces different kinds of thinking. Every millimeter matters. Every component choice cascades into consequences. But there's also something deeper: the fantasy of having genuine computing power in your pocket, or in this case, in your wallet, without the bulk of a phone or even a smartwatch.
Krauseler has published the schematics and design details on GitHub, making the project reproducible for anyone with the skills and patience to attempt it. They've thought through several potential applications. A smart home dashboard that lives in your wallet seems impractical until you imagine showing someone your home's status without pulling out your phone. A two-factor authentication device that's always with you, in the same place you keep your actual cards, has a certain elegance. A digital wallet for NFC tickets and passes—concert tickets, transit passes, event credentials—could genuinely replace the paper and plastic you currently carry.
But here's the honest part: Krauseler built this because they could, because the constraint was interesting, because the question of how small a computer could actually be was worth answering. The practical application came second. Now that the device exists, they're asking the community what it should do. It's a refreshing kind of honesty in maker culture—the acknowledgment that sometimes you build something first and figure out its purpose later. The technology is ready. The form factor works. The question now is whether the world has been waiting for a credit-card-sized computer, or whether this is the kind of thing that will find its use case only after someone sees it and thinks, "Oh, I could use that for..."
Citas Notables
I wanted to build a smartcard that is actually the size of a real credit card—including the actual thickness— Krauseler, maker
La Conversación del Hearth Otra perspectiva de la historia
Why build something this small if you don't know what it's for?
Because the constraint itself is the interesting part. Once you've proven it's possible, the applications start to make sense.
But there are already card-sized devices out there. What makes this different?
Those devices claim to be card-sized. This one actually is—same thickness, same dimensions. It's the difference between "almost" and "actually."
So it's about honesty in design?
Partly that, but also about what becomes possible when you stop compromising. A real credit card thickness means you can't cheat with extra bulk.
The NFC chip seems like the most practical part. What can you actually do with that?
Store tickets, passes, authentication credentials. Anything you'd normally keep on your phone but want to carry physically.
And if someone actually uses this as a wallet card, won't it break?
That's the real question nobody's answered yet. It's a prototype. Durability in actual use is different from durability in a lab.