Electronic voice phenomenon (EVP) is  very common in a active haunting. This activity is captured when a recording device such as a digital  recorder is used to record disembodied voices in an area that is thought to be haunted .Many times , the human ear cannot hear these voices.  We here at POST believe that EVPs originate in the lower frequency zone below 50hz. 

  We have documented many of these phenomenons in our investigations. It is believed that most evp’s come from an intelligent type haunting.

Important things to remember while conducting an evp session are .
#1 After asking a question leave enough time for a response.
#2 Always be mindful of who is in the room at the time of the session (make a note on the recorder).
 #3 When asking questions or talking, speak at a normal level (no whispering).

Most of the evp’s that have been encountered have had a whisper quality about them; as if someone standing close to the recorder whispered something. A lot of the evp’s come through in a simple one word form, such as "yes" or "no". The best evp’s are in response to a question and clearly state a whole sentence and not just a word. Complete sentence’s like "I did not jump" or "I hate the back bedroom" are proof that it was not just a "noise" that sounds like a word, but an intelligent full spoken sentence.

Electromagnetic field (EMF) is basically a flow of energy. The earth has its own EMF which can spike and is constantly moving. EMF can produce negative feelings in people  (electro sensitivity). Some people may be more sensitive to this field then others. It can produce the feeling of paranoia, nausea, headache, and the feeling of being "watched". In fact, some accounts of paranormal activity have been linked to high EMF readings (not a haunting at all). Fix the high EMF reading and all the negative feelings and anticipation are gone.

On the other hand, Spirits or Ghost are believed to  give off an EMF reading, due to the belief that they them self’s are pure energy. As I said before in the residual haunting cases; the current quantum view is that "we are essentially electrical beings existing within the electromagnetic embrace of the earth". It is also believed that Spirits can draw energy from alternative sources such as batteries, people and the very air around them in order to manifest. This is the reason for cold spots in the vicinity of paranormal activity.

We use several types of EMF gauges or milligauss readers. One gives us a digital EMF reading and temperature reading simultaneously on a back lit screen. The other simply gives a reading of the EMF strength. However the EMF gauges are not solely used to prove or disprove Ghost or a haunting, due to the fact that natural EMF is everywhere. When you combine a notable EMF spike with other instruments, such a temperature gauges & you record a drop in the ambient temperature or an anomaly captured on video or audio at the same time, then you might be onto something.