I think ghost investigation-ers (no, not investigators) just have the wrong idea of how to look for ghosts.
If I was searching for evidence of ghosts and had the time and money to actually pursue it, I'd take a completely different approach.
First! I would look for the least haunted place on Earth. I would conduct all of my tests there to establish a control... a baseline.
Why jump through hoops to get my ass haunted by some demon at an abandoned asylum if I can get the same experience at home, in my PJs, with a bag of Doritos? Not to mention, if there's no difference between my livingroom and that asylum, then either ghosts are equally distributed across the world, or they don't exist.... or some weird shit went down in my livingroom at some point in the past.
Next! Lose the hokey "spirit box" crap unless you're in a faraday cage.... no... lose it altogether.
Energy cannot be destroyed. It can only change form. So, if ghosts are real, stop scanning for voices and spoopy stuff. You need to track energy transference. Every hinged and loose object needs an accelerometer attached to it. Tie the sensors into a Wii game, and stream the thing on Twitch as "Ghosts play Smash Bros" or something. That should help finance your investigations.
3D thermal cameras covering every inch of the place. Sensors for seismic vibrations. External microphones and cameras to be used to keep track of possible outside contamination.
No people. Nobody goes into the place. Who knows what kind of butterfly effect just walking through a room could have. A dudebro screaming into the darkness on one side of the asylum turns into a demonic possession by the time the scream reaches the other side of the building.
I could keep going, but I just realized how long this went and I have no clue why I'm still writing. I just wanted to make the point about establishing a control, and I guess I got carried away.
