BrakeFree The Smart Brake Light for Motorcycles
This won't be available till April 2018 but I pre-ordered mine. No wires or apps with an 8 hour battery life. Accelerometer and gyroscope sensors detects braking, downshifting and more. My theory is whatever makes you more visible and it only weighs 6 ounces.
https://igg.me/at/brakefree/x/16458078
Been available for quite awhile
Wireless brake lights mounted on helmets actually have been around for quite awhile now. I used to use one similar to this; several years ago, had them on a couple of helmets:
https://www.youtube.com/watch?v=v009kRAHMSk
Do a search for motorcycle helmet brake light systems:
https://www.google.com/search?q=wire...e+light+system