Experimental equipment is using things we have laying about to see if anything useful can become of it.
The Yamaha digital mixing desk and the multi- track analogue recorder. With this set up we can place multiple microphones throughout a location and monitor them all from one place, and record them all as individual audio tracks all at the same
time in full professional level audio quality.
The i software
There are many interesting Apps available, not things like ghost radar but apps like the seismograph, which can detect vibrations, or applications such as the various audio level indicators which can detect is in fact there was a sound or a knock etc. there are new apps all the time and
its worth showing some imagination and applying them to your investigations.