Ledger, Trezor, Tangem — every one of them needs a host. This one doesn't. It has its own screen and its own radio, so it shows you the address and signs it, on its own.
Every layer is fixed. The display is the largest single item.
The touch is not decoration. The card takes a PIN and shows an address, so it needs a real on-screen keyboard. Segment displays and button interfaces are out.
The parts are on a development board right now and we're measuring current draw phase by phase. What we want to know is what kind of storage this card actually needs — and whether it can hold a week of use with nothing but a windowsill to recharge from.
Our load profile is the inverse of yours.
PaperiNode runs a short cycle every few minutes, forever. A supercap under harvest fits that perfectly.
A wallet card sits untouched for weeks, then does everything at once — wake, attach, fetch, render, take a PIN, sign, sleep. Then weeks again.
That breaks both options.
Self-discharge is the same order of magnitude as our entire sleep current. A month in a pocket and it's flat on its own, with the card having done nothing at all.
It holds charge for months, but at that thickness the internal resistance is high, and NB-IoT pulls hundreds of milliamps on transmit. The rail sags — worst case, a brown-out mid-attach.