I just LOVE seeing such hacks. Boy wants something, boy looks around, boy finds parts to hack, boy makes! Stonioni did precisely this! He wanted a bicycle battery-free safety light, so he hacked an old HDD to get the magnets, he chopped a relay to get the coil, some wooden icecream sticks, a batch of LEDs, mounting staff and that's it! Amazingly simple and yet so effective. The magnets are mounted on the wheel, and as they pass in front of the static coil it generates all the power needed for the LEDs to blink. The faster you go, the faster they blink.
I mean, check out how he mounted the magnets on the wheels... So simple yet so cool! Glue the magnet on an ice cream stick, cover it with heatshrink tube, use tie-wraps to mount it on the wheel... Perfect
My addition (as an EE) would be some sort of capacitors (maybe an ultracapacitor) and a tiny micro-watt LED flasher to have stable rate of flashing... But i Love it! Good Job neighbor (he is from Italy)