The Kickr turns any bicycle into a stationary trainer by replacing the back tire. When a rider using its accompanying app meets a “hill,” more power surges through magnets in the Bluetooth-connected device, creating a stronger pull on its flywheel and increasing resistance. Wahoo Fitness Kickr Power Trainer $999
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.