You could take a homogeneous gas, use the demon to separate it in hot and cold (using no energy), then use the temperature difference to perform useful work (wi

You could take a homogeneous gas, use the demon to separate it in hot and cold (using no energy), then use the temperature difference to perform useful work (with any number of engines, such as Sterling's), then use the demon again, and hey presto, you got yourself a perpetual motion machine. (BTW, one can buy Sterling engines, some of which work with body temperature, ie holding it will create enough temperature difference to turn the engine: https://thestirlingengine.com https://thestirlingengine.com https://www.stirlingengine.co.uk/default.asp https://www.stirlingengine.co.uk/default.asp https://en.wikipedia.org/wiki/Stirling_engine https://en.wikipedia.org/wiki/Stirling_engine )