Cards
A card costs about twenty cents and holds a 64-bit number. Here is exactly what goes on it, and a writer that puts it there.
Make a card
What that produces
Two NDEF records. The first is a URL, so that a card found under the sofa and tapped on any phone — no app, box switched off — opens this page and says what it is. The second is the compact record the box reads.
…
Why so small?
Because it has to fit an NTAG213, the 20¢ sticker, which has 144 bytes of user memory. That is not a limitation we are working around — it is the design. A minute of a parent reading is 183,600 bytes; the biggest cheap tag on the market holds 0.3 seconds of speech. So the card is a pointer and the box owns the audio, which is also how a Toniebox and a Yoto card work. The full argument, with the table.
| Tag | User memory | Fits a tape card? |
|---|
No Web NFC? That is the normal case
Writing tags from a browser works on Chrome for Android and nowhere else — not Safari, not iOS at all, not any desktop browser. So the box writes cards too, and that is the primary path rather than the fallback: in the studio, press enrol a card, put a blank card on the pad, and the box writes it. Your phone only ever needs a microphone.