Electronic Voice Phenomena (EVP) typically uses acoustic measurement to record "voices from the other side". Sometimes they capture interesting snippets of sounds corresponding to partly discernible human voices.
I find it somewhat difficult to see how an unseen entity can impart communications to an electronic storage device (and then through a microphone and stored on tape or digitally) without being heard by the human ear mechanism (which is really very sensitive - it can detect an ear drum vibration similar to the width of a nitrogen atom) but let's assume such is so. I wonder then if an optical channel would be easier for such entities to access?
The early movie theater films for example, used an optical transducer (a "Kerr cell" from memory) to reproduce the sound track. These days we could just use a photo-diode or photo-transistor to record light variations. Would an optical EVP better suit the interception of such communications if these exist? Given that "ghosts" are more often seen than heard, perhaps an optical detector would be better suited for such research projects?