Wen signing a txn with a sound that plays from your signing device? I can see this happening.
No need for nfc, cameras, Bluetooth.
Discussion
1990s modem sound
That was exactly what I thought of at first. 😂
I wonder how short the sound could be.
All of that modem sound was the handshake stage, so I guess a TX would be similar. Can't really get more inefficient than sound.
For air gap signing:
Camera is bad in very dark or light conditions
Bluetooth I don't trust
Micro sd is a bit clunky
Nfc is good but need to be close enough to the receiver and have the ability to read.
Sound- everything has a speaker and microphone.
Just thinking aloud
Here's a fun one. Direct line of sight lasers.