ChatGpt gives this summary
➡️ Without internet
SMS relays (TxTenna, mesh networks)
Radio broadcasts (ham radio, Locha Mesh)
Sneakernet (USB stick, QR code printouts)
➡️ Without computer
Hardware wallet + microSD / QR code
Possibly hand-written transactions (practically infeasible)
With all of these, at least one party must have access to the internet.
Physical cash on the other hand works while both sender and receiver are 100% offline.
That’s not correct. The Bitcoin network itself eventually needs internet to confirm a transaction, but neither sender nor receiver needs direct internet access. A signed transaction can be broadcast by any third party (e.g. via radio, SMS relay, or satellite uplink), similar to how a cash payment can later be deposited at a bank.
