Ask HN: Could phones be quietened automatically on trains?

There is a long answer, but in the main the sound you get finally goes though an analogue amplifier. There is no way to know what volume it uses. Controls say quieter or louder, but not how loud loud is. For example for earphones loud is comparatively quiet. So it's hard to know what you could do, Bluetooth volume would mean nothing.

Happens once in a while on the municipal bus here in Tompkins County and for a while we had somebody who watched videos on their phone that sounded like AI slop with maudlin sentiments and the vocal equivalent of large type in the area of the gas station where you might drink your coffee or eat your pizza slices.

Could be done with low energy Bluetooth beacons on the bus or something like AirTags. Such a beacon system would also give accurate position on the vehicle which would open up other location-based services (go three cars forward for the restaurant car)