Paranormal Investigators use many of the techniques and equipments for Spirit Communications. But now a days, they are using a device which is a Spirit Box.
A Spirit Box is an audio-only device that rapidly scans through multiple audio channels that is said to make it relatively easy for ghosts to manipulate to say a word or phrase in real time. It has been proven that sounds other than spoken language can be captured on the spirit box and is usually discovered as something other than what is surrounding the investigator.
A Spirit Box uses white noise as a medium to communicate with spirits. white noise is a random signal having equal intensity at different frequencies, giving it a constant power spectral density.