Most of the devices/ concepts that aim to use human power to generate power or charge batteries require people to go out of their way to do so. Not making people do that is what makes the Jumping Light skipping rope an interesting concept.
Designed by Hyun Joo Lee and Eu Tteum Lee, the Jumping Light is quite like any other skipping rope, except that the ends of the rope include flashlights. A system in these flashlights stores the kinetic energy generated during the exercise/ jumping and converts the same into electric energy that lights up an LED in the flashlight.
To make it more useful, there’s a counter to show the number of jumps, and an indicator to show the charging status. The weird part, though is when the designers talk about the LED flashlights being helpful for when you decide to exercise in the dark! That really puts a twist to this conceptual tale.