I made an iPhone app that shows your next train station in the Dynamic Island and lock screen. What makes the app unique is that it appears automatically when you're riding a train; you never have to open the app.

It only works in the Tokyo/Kanagawa/Chiba area of Japan, but I'd be grateful for any fellow train riders here to give it a go (the UI is in Japanese and English).

I wrote a bunch more about my motivations for creating the app, its current limitations, and ambient computing on my blog [1], along with some devlog posts [2] [3] from the past few months.

The train tracking algorithm turned out to be a lot more difficult than I expected and is very much a work in progress. If anyone's come across any research about ways to synthesize flakey GPS data, device accelerometer data, and static/dynamic train timetables, I'd love to hear about it.

Happy to answer questions too.

- Chris

[1] https://twocentstudios.com/2025/06/03/eki-live-announcement/

[2] https://twocentstudios.com/2025/05/29/train-tracker-devlog-0...

[3] https://twocentstudios.com/2025/04/15/train-tracker-checkpoi...