An EMF listening device is a special microphone with a dedicated pre-amp that is able to capture the Electromagnetic field in the spectrum of the VLF.
The LOM ecording label and instrument maker, made both a DIY kit and an already made instrument for it and it's called Elektrosluch.
Unfortunately, most of the amazing instruments made by LOM goes out of stock really fast. However, they kindly provide the schematics for the Elektrosluch DIY.
This DIY EMF listening device is the main recording means used for recoring the album Elettromagnetica.