If you just want something that flashes...

Try the ReeLight induction lights.

SL200 set - Reelight ApS

I believe the 100 model only lights with motion. The 200 model has a bit of storage power so it continues to flash while stopped at stop signs or lights.

Mount them on the bike, then forget about them. There are several models. The flashers won't illuminate the street, but will help a person be seen (use street lights to see by). There may be more powerful models to also see with.