Yes, you have to push the button to access it after, but it's always recording up to the length of it's buffer (which depends on how much RAM you have installed). From my very hazy, vague memory it was ~5 minutes.
This was a big concern of mine too. That's why as much of Jamcorder as possible is open standards.
There is also a local web interface, http://jamcorder.local, that is fully extensible by the user. And the BLE and Wifi APIs are not locked down. You can implement your own app.
The biggest limiting factor IMO, are Wifi and BLE still going to be in common use in 30 years? That's hard to predict. But the SD card will still be there. Its a tough problem.
I think that's about as good as you can do, short of putting a screen on it.
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There's even a feature identical UART interface for the device. Surely that will still work in 30 years.
It seems the biggest future proofing thing is that all recordings are just written to an SD card. So even if the app doesn't work at all, you can always pull the card and read data off there.
It was the first information I wanted to know, but it wasn't in the article.