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?

Embedding crypto signatures in audio sounds very fun. I’m imagining R2D2-like conversations or call & response melodies.

seen a couple ultrasound signatures in audio content today, but not very well. variable streaming quality blows up the signature