Interesting! I've never had success triggering them, though that's not surprising given I'm on an aluminum and carbon frame.

There was actually a kickstarter a few years ago to build a magnetic loop you could put on your bike to trigger the sensor via a button press, but unfortunately it didn't meet its funding target and seems to have gone underground: https://www.veloloop.com/faq/

If you've got metal rims, and the loops are reasonably tuned, you should be able to trigger them if you're well positioned. Apparently, adding a copper wire loop under your rim tape will work for carbon fiber rims as well.

There's some pretty good information here: https://www.bikewalknc.org/bicycle-detection-at-traffic-sign...

But I've been lucky enough to have California government on my side, I guess.