Device-to-device audio communication (think QR codes, but made out of sound) seems very underrated. Much better UX than QR codes or NFC because you don't have to worry about putting your phone in the exactly right place or pointing it in the right direction.

Anyone here with more detailed takes on this?

Is that not precisely what is getting exploited in this scene from Hackers:

cult classic cryptoartist
linktr.ee/sgt_slaughtermelon

I love the idea of redboxing an Ethereum transaction 😆
Also my phone making old school dialup modem noises anytime I buy something.