This is a brand new, unused LED tail light (rear light) with a solar panel (no batteries required). It automatically turns on when it detects vibration and flashes red. It automatically turns off when the vibration stops. It attaches to the rear fender. This product can also be used as a replacement for genuine tail lights on electric assist bicycles from manufacturers such as Panasonic, Yamaha, and Bridgestone if they are damaged or broken. I think it would cost nearly 3,000 yen to have it replaced and installed at a bicycle shop.