Pictured here is a K-II (K2) Meter and it is, basically, an EMF Meter.  They're better suited to this purpose than standard EMF Meters primarily because of the colored light display.  Not only is the display more easily seen than that of a standard EMF Meter, but as a result of the color scheme of those lights it theoretically displays the approach and withdrawal of the entity in question.  They're often successfully used in EVP sessions when the lights seemingly respond to questions posed by the investigator(s).

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