Here's another concept for you.
In addition to the LED brake strips on the back of my bikes, I also run a Brake Free light on the back of my helmets.
This is pretty clever. It has multiple settings to run as a regular taillight with full or partial LEDs, and an accelerometer that detects deceleration and kicks all of the LEDs on full bright when you slow down.
You attach a mount to the back of your helmet that sticks with 3M tape, and the light clicks into the mount. I have multiple helmets and swap the light to whichever helmet I'm going to wear. A charge lasts a long time - I'll charge it every week or so if I remember to, and it flashes one of the LEDs when you start it to indicate the battery level.
I can't see the back of my head to verify that it works, but a rider in my neighboring office has one too, and I can see it kick on when he slows, even before his brake light comes on.
https://www.brakefreetech.com/