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Comment by vanilla_nut | Hacker News Reader

One more reason I'm glad I connect my phone with a headphone jack. Just an analog connection carrying audio. The car doesn't even know what it's playing, as far as I know. Though some cars do seem to extract track names and artist names over the aux jack, so I think there's a little more than just an analog signal?

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An analog jack should just be an analog signal, the beauty of it for applications like this being that it just works and for a variety of devices including the very first Sony Walkman to name just something which did not include any extra information. While in theory it is possible to encode extra and inaudible information in there, it seems more likely that if a car then knows what is playing it is just using Shazam or similar.

Possibly a side channel digital encoding of the track information, similar to how radio stations can display things like track name on your car radio. But I'm not really sure.

I wonder if phones send out RDS (https://en.wikipedia.org/wiki/Radio_Data_System) information on the aux jack and your car happens to pick up on it.

This sounds like the content recognition they do on TVs. If that's the case, this is creepy as fuck.

One downside I see to this is it being illegal to use a phone while driving, but interacting with your car stereo is fine.

Now I'm wondering if any car stereos have four-pin aux inputs to send headset button inputs or microphone audio back to the phone.

Audio jack can be used for Square payment transactions so it can't be that isolated

Do you mean the thing for reading a magnetic stripe? It's no surprise that can be trivially sent over an audio interface. That's how recording audio onto tape works in the first place.

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