An EMF meter is used to examine the electro magnetic field in the area. Paranormal investigators believe that when you are in the presence of a ghost the readings will on the EMF detector will increase.
EMF meters should be turned on throughout an investigation and whenever there is an unusual reading they should be cross referenced with any other instruments in use such as a digital recorder.
How To Use An EMF Meter
I think the analog meter is the best EMF meter. The best way to use an EMF meter is to hold it at the base. It should be cupped in your hand this way it does not obstruct the sensitive sensors towards the top of the meter. For the best readings it is highly recommended that you remove all jewelry such as rings, bracelets and watches that sometimes can interfere with the meter.
To get use to your meter I highly suggest that you use it around your home to measure electrical wiring, outlets, and yes even light fixtures. While your at it get use to measuring other electronic equipment such as stereos, clocks and microwave ovens when in operation. This gives you a good idea of the background levels of Electromagnetic pollution these devices generate. Even measure stray electromagnetic fields that can be induced into copper or iron pipes that carry water will give you the a good idea of how sensitive these meters can be.
Why do you want to do this? Well so when your out ghost hunting you can deduce or decide whether you have a false positive reading!
Yes older buildings buildings tend to collect more ghosts but older buildings also have older electrical systems that sometimes have bad wiring, unshielded wiring or ungrounded wiring thus leading to more false positive. Using an EMF meter is just a tool. Once you get use to the meter it is more of an art that a science when drawing conclusions on a ghost hunt.
Here’s a cool video that compares some of the leading EMF Meters on the market.