Kingpin;140869
Well, as a description of what it did wasn't given, it may not have been meant to be a gas sniffer in the film universe.
I wonder where the Ghost Sniffer name came from… if it was from something official or if it just got called that by the fans.
In the commentary of the first movie Ivan Reitmen mentioned that they has a real person who studies the paranormal such as ghost come in and help discuss what kind of props the ghostbusters might use to find ghost.
He mentioned that the guy said that you might find changes in the electric field or possibly some oders that might be present. They then asked Bill to look at these “equipment” they had and asked him to pick out the funniest looking prop to which he chose that “sniffer.”
Yes it is a sniffer that detects gas leaks, but a ghost catcher might be able to use it to detect the residues of a nearby ghost. I also believe Harold called it a “ghost sniffer” a few times.