[ramses0]

Take a look into Lumos bike helmets: https://ridelumos.com/products/remotes-and-mounts

They started via a kickstarter in 2015: https://www.google.com/search?q=lumos+helmet+history

...they kindof "always" had reliability issues w/ detecting braking accurately, I think switching between the handlebar remote/sensor or phone sensors. It's an existing product with a direct analogue to your project goal, and minimally you could trawl for contacts within customer reviews or online reports to get some ideas about the good/bad in this problem space.

Beware of patents (as relevant), but it's a noble and useful project and goal.