Another possibility is tapping into other magnetic fields. I remember hearing of a device that appeared to produce free energy. The creator new this was impossible, but there it was. He took the device to a friend to demonstrate it and it didn't work. They finally figured out that it was his house's proximity to high voltage lines that made the device work. It was tapping energy from the changing magnetic field from the lines. By no means free, and often illegal if used to steal energy from the system.