Perpetual motion machines work by the following mechanism:
* "Inventors" come up with some razz-matazz to convince fools
that they have a perpetual motion machine that actually works.
* Fools give the "inventors" money.
At least USPTO have *finally* stopped accepting patents for perpetual
motion machines. The purpose of these scams is to separate the credulous
fools from as much of their money as possible. It works only too well as
the latest incarnation called eCat demonstrates so well.
Since the function of the invention is to separate fools from their
money, they only need to generate the illusion of energy.
Not even that. People will believe what they want to believe
irrespective of powerful scientific evidence to the contrary.
The closest I have seen to a perpetual motion machine is an
electrostatic Zamboni pile and an small piece of aluminium foil. They
were used to power first generation night vision equipment. The foil
jumps to and fro until metal fatigue gets the better of it. Total output
power is in the low 100s of nW.
The Oxford electric bell has been powered by one since 1840.
http://en.wikipedia.org/wiki/Oxford_Electric_Bell
I think there is another somewhere using a sulphur ball and friction
also in hard vacuum not been running quite as long. It made the news a
decade or so back when an industrial dispute threatened to deprive it of
the LN2 needed for the hard vacuum cold trap.