Bremen-based designer Dennis Siegel built special devices that are able to tap into several electromagnetic fields to exploit them, where the energy is stored in typical batteries. Users can then retain the charges from the power supply of any machine, a cell phone or the catenary of a train by holding the harvester directly into the electromagnetic field whose strength is indicated by a LED on the top of the object.
Depending on the strength of the electromagnetic field it is possible to charge a small battery within one day. The system is meant to be an option for granting access to already existing but unheeded energy sources. By exploring these sources it can create a new awareness of the invisible electromagnetic spaces.
Read more at his website: http://dennissiegel.de/electromagnetic-harvester/