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?

Some physical store tried this almost 10 years back. Walk in to a specific section of store, install app, will capture Audio signature and give rewards. Kids recorded the audio clip being played and farmed 😂. Idk it seems QR code is much cheaper for places like India. Audio will need an emitter as well. Cost.