Adding encryption shouldn't be hard, as long as you can communicate the keys out of band.
Could probably achieve the same result using audio instead of video, but maybe that would be too annoying?
https://en.wikipedia.org/wiki/Timex_Datalink
It'd transfer phone numbers and calendar entries to the watch by blinking the screen of your computer. Kinda a 1 pixel version of this.
(I wonder where that ended up? From memory I threw it in a drawer when I finished the Windows 95 project I'd been working on, and switched to Mac. There was no Mac software to talk to it.)
If your firmware is small enough to fit that model, it isn't a bad variant. Beats downloading a file, transferring it to a USB drive, sticking that in,...
Probably still wouldn't want to use digital audio input though. Although it's a perfect digital stream, it's been processed in analog-like ways before it gets to the device - such as filtering and volume changes. So you'd still want to use a modem protocol over it.
1998 - https://groups.google.com/g/comp.sys.psion.misc/c/oFtTHyx6IR...
Airdrop is a thing, but remember that Android phones are controlled by the online services company that wants you to use online services.
Do you mean the one that went to all the trouble to reverse engineer Airdrop so that people could access Apple's vendor-locked walled garden without the use of online services?
It's interesting that you learn to recognise patterns in the burbling tones after a while. "CQ CQ CQ" is very distinctive and after a while you can hear your own callsign in it. I guess it's not that different to very fast Morse.
Usability is important though. If you have to type in a bunch of hex digits before sending, it won't be used.
The same way you whisper to say something secret in a public space I would expect people who transfer something private in public would have the presence of mind not let other snoop on and react accordingly.
Bringing it into the ultra sonic band would help.