Originally Posted by
Morelock
https://vervecycling.com/dig-deeper/
This seems to imply that they do use magnet/reed switch, although in the past I am pretty sure I had heard it used an accelerometer. Not sure...
You are correct. There is a magnet:
InfoCrank uses a reed switch, triggered by a fixed magnet mounted on the bike frame.
All Reed Switches are activated by magnets, including SRMs.