An LED on top of the harvester indicates the presence and the strength of an electromagnetic field. There are two types of harvesters for different fields: a smaller harvester suitable for lower frequencies below 100Hz which you can find in the general mains, and a bigger one that can be used for lower and higher frequencies like radio broadcast, GSM, Bluetooth and Wireless LAN.
For recharging purposes for portable consumer devices such as smartphones and photo cameras, this invention could become very relevant. Imagine yourself waiting for an important call while your battery is draining and your charger isn’t there to help you. Particularly when integrated in a phone, energy harvesting will make it possible to just reload your phone by having it somewhere close to a electromagnetic field. The city is the charger of the future!