EMF Meters (Electro-Magnetic Field Meters)
If someone is getting unusual EMF readings in an area with no explainable reason found for the unusual readings, take photos/video/EVP/etc. You may capture something.
But be careful, because just about everything that runs on household electricity, as well as battery powered devices, radiate EMFs. You must keep a lookout during an investigation for sources that could be radiating electromagnetic energy. Scout out the area first to locate any sources that may cause EMF's, so while investigating you'll know where these are located.