The K-II meter was first introduced to the Ghost Hunting community back July 2007 on Ghost Hunters episode 312 The Manson Murders by guest investigator Chris Flemming, before that time it was a cheap $30 EMF detector made by  K-II Enterprises a company that also makes dog trainers. Overnight this dectector went from $30 to $60 and was touted as a tool that could be used to communicate with ghost. After the public began using the device it was soon discoverd how easily one could get fake responses from the device by operating the pressure sensitive swiitch as well as some interesting facts about its sensitivity.

It is advertised to operate accurately in both the range of 50 to 1,000 Hz as well as 1,000 to 20,000 Hz which is essentially most of the audio spectrum. Because of its relatively high range (it starts at 50 Hz) it will miss 90% of the frequencies associated with paranormal activity, except for specific EVP work. The other problem with the meter is it is unshielded to the point of where any EMF source creating harmonics within its bandwidth will set it off. Radio transmitters, cell phones, you name it, the KII will respond, not to the fundamental frequency, but to its lower harmonic frequencies. Because of this, it is useless for exact EMF field readings. 

For a good explanation of how Ghost Hunters faked evidence with the device click on this link here .  A full review and test of the K2 meter exposing it's many flaws and explaining how it should never be used in any serious paranormal investigation.  Read the article here  Addressing The Safe Range EMF Meter.  Article written by Kenneth Biddle of The Paranormal Research Investigators Association.