Free energy suppression (or new energy suppression) is a conspiracy theory that technologically viable, pollution-free, no-cost energy sources are being suppressed by government, corporations, or advocacy groups. Devices allegedly suppressed include perpetual motion machines, cold fusion generators, torus-based generators, reverse-engineered extraterrestrial technology, anti-gravity propulsion systems, and other generally unproven, low-cost energy sources. Claims of suppression include: