Free electricity for a bicycle headlamp
A really good bicycle headlamp needs quite a bit of electricity to make it bright and last a couple of hours. A dynamo requires extra leg power to operate. Yet, there are power distribution lines along the roads where I ride and they emit electro-magnetic lines of force. Imagine a coil of wire on the bicycle that follows the triangle portion of the bicycle frame and it receives these lines of force, converting them to a low voltage AC current. That current would then be passed through a bridge rectifier and a voltage regulator to charge normal size flashlight cells powering the light. Technically, it is probably illegal. Certainly it would be if you were using a coil of wire on your lawn positioned under the power lines to power your house. If it could be done safely, the power company would have a hard time tracking you. It is probably impractical, but it is interesting to ponder.