I just read an article in a magazine about data over sound.
Some apps use ultrahigh frequency sound to commuicate with other devices without being recognized. This works even if the device is in Aeroplane Mode since it only uses microphone and speaker.
You can control the microphone on android, but you can’t control the speaker so every app can use your speaker to send out data without you recognising it.
I’m not really sure how /e/ can handle this but i think it should do.
Maybe you have ideas.
Sources (beyond others):