With the SL-120 set, you get front (white) and rear (red) LED lights and four magnets. The lights attach to the axles of the bicycle, making them much more difficult to steal than conventional LED bike lights. The magnets attach to the spokes (2 on the front wheel, two on the rear) and generate a current in the light every time they pass it. You never need batteries! These lights run on bicycle power. The lights flash steadily, and keep flashing for about two minutes even when you are not moving. They are very durable and can be used in any type of weather.