Dive Summary:

• Dennis Siegel, a student at the University of Arts Bremen in Germany, claims to have built a portable electromagnetic harvester, which can gather ambient electricity from power lines, trains or coffee machines, and charge AA batteries.
• "There are two types of harvester for different electromagnetic fields," Siegel writes on his website, "a smaller harvester that is suitable for lower frequencies below 100Hz which you can find in the general mains (50/60Hz, 16,7Hz) and a bigger one that is suitable for lower and higher frequencies like radio broadcast (~100MHz), GSM (900/1800MHz) up to Bluetooth and WLAN (2,4GHz)."
• The wireless transfer technology he uses appears to take about a day to charge a AA battery, depending on the circumstances, but his concept could have interesting practical applications on a larger level or with multiple devices.

From the article:

"... As a concept, though, Siegel’s electromagnetic harvester is very interesting. On its own, a single harvester might not be all that interesting — but what if you stuck a bunch of them, magnetically, to various devices all around your house? Or, perhaps more importantly, why not use these harvesters to power tiny devices that don’t require a lot of energy? Sensors, hearing aids (cochlear implants), smart devices around your home — they could all be powered by harvesting small amounts of energy from the environment. ..."