There are multiple NFC cards, I think it's using Shamir secret sharing to reconstruct the secret. The keynote video is pretty instructive. A lot of marketing (as it should!) but nevertheless explains all the great tech they are using. Super damn impressive.

Foundation

Passport Prime

also i would really like a device like a yubikey that works for nostr, so it's NFC as well as USB and at least uses a 6 digit pin to encrypt the keys, or better, is actually a full bip-340 signer inside so it demands a pin to unlock the stored key and then after some configured amount of time or when unplugged the decrypted key is lost or nuked

You are correct

That's the beauty of Prime, anyone can build that app for our hardware.

oh, it's not just a NFC card it's a fairly large piece of hardware it's a bit bulky, have you got plans for something smaller, maybe even doesn't have any inputs except maybe a button and an indicator light? also, what protocol is it working with? i quite like the concept of a device that has only NFC and USB and no wifi or mobile radio that is just for keeping my keys secure though, i could maybe go for this especially if i can use it to replace my whole login flow for browser and pc (linux)