I see I'm not the only one who uses quotes when talking about "ghost hunters" or "paranormal investigators". If they weren't dressing up as ghostbusters on a Friday night, they'd be in the woods, dressed as Hobbits on a Saturday afternoon. It's not science. They find any random piece of equipment that's already known to give anomalous readings from time to time, declare those readings to be the result of ghosts, and then walk around pretending to be scientists. They make completely unfounded statements like "Ghosts give off electromagnetic fields" just to justify waving around a cheap piece of equipment that's guarateed to give them at least one "ghost" per hour. That's simply not how science is done. You don't get to just invent a property of something just so you can go looking for it. "My batteries died - therefore: ghost"
It's a lot easier to find what you're looking for, when you get to be the one arbitrarily deciding what is and isn't a sign that you're getting closer to the thing you're looking for.
You know when your shower head spits air randomly? That's it measuring my awesomness. It can be detected from very far away.
Here is a good explanation from Dave Schrader