A perpetual motion machine is a machine that exists in a constant state of motion with no supply of energy. They are forbidden by many fundamental physical laws and can not be created, no matter how complex or ingenious the design.
Many attempts at developing perpetual motion machines have focussed on the use of magnets. Magnets can influence the motion of objects at some distance with seemingly no input of external energy. However, the mystic and sometimes counterintuitive properties of magnetics are also governed by the same physical laws that everything else is, including the First and Second Laws of Thermodynamics.
Almost always a magnetic perpetual motion machine consists of some variation of position and geometry of static and moving magnets. There are many examples of purported magnetic perpetual motion machines that can be found easily on the internet. Each one of them can be discredited by looking carefully at the system as a whole. If the starting motion is created with a nudge of the hand or a drop through gravity this is an input of energy which will slowly but surely dissipate. Any perpetual motion machine will grind to a halt with the addition of a load needed to extract work. Both the US and UK Government officially recognise the non-existence of perpetual motion machines by automatically rejecting patent petitions for devices claiming to demonstrate perpetual motion, with the UK patent office stating "articles or processes alleged to operate in a manner clearly contrary to well-established physical laws" are "regarded as not having industrial application".