Allegedly, by patenting different parts of it - because patent offices do not accept claims for perpetual motion machines. Of course, nobody has ever built one, otherwise we'd all be riding around in electric cars powered by infinite supplies of electricity.

The UK Patent Office notes that you cannot get a patent on "articles or processes alleged to operate in a manner clearly contrary to well-established physical laws" as they are "regarded as not having industrial application". Any machine that generates more energy than it consumes is either a nuclear reactor or breaches the second law of thermodynamics.

But the Irish company Steorn, which has brought attention to itself by claiming to have a magnet-driven machine that will generate more energy than is put into it (and has taken out an expensive advert in The Economist rather than publishing a scientific paper or even building a few prototypes) says it will get around the restriction on patenting its invention by splitting it into components and patenting those. Then, by assembling them, it will have a patented energy generator.

The machine, though, isn't a reactor. Quite apart from the question of whether Steorn has invalidated its own attempts to get any sort of patent by showing it off to the Guardian (These men think they're about to change the world, August 25), there is the knotty question of whether it can sneak the pieces past the patent examiners' eyes to be assembled, with patent protection, to produce a machine that squares the circle of producing energy for free while also being under patent.

Confusingly, the company's website (http://tinyurl.com/mdt5e) says that the design of the "free energy" generator is "patent pending", but the World International Property Organisation (WIPO) publication WO 2006/035419 indicates that the patent on a "low energy magnetic actuator" has only been applied for, not granted by the US Patent Office - and a search of the USPTO database confirms that.

Meanwhile, plenty of scientists appear to be lining up to put Steorn's claims to the test. The company claims that more than 3,000 have already applied to put its "free energy"device through rigorous testing: it has set a closing date of September 8, after which 12 will be invited to test the equipment. "The results will then be published worldwide," Steorn says, at which point either the doubters will be left with a lot of egg on their face, or - on the balance of history, almost certainly - the eager inventors at Steorn will.

Still, assuming that the USPTO awards the patent, Steorn will at least be able to tout a low energy magnetic actuator to anyone who wants one. It's not free energy - but if you're trying to patent a perpetual motion machine, you clearly weren't about to give the energy away for free anyway.