Egon's Probe is a makeshift video camera mounted on a miniature helicopter and tethered on a cable line.
During the case at the Von Limburger Mansion, the Ghostbusters were stumped with a supernatural hole. Egon Spengler decided a probe needed to be sent in. From a mobile monitoring station, Egon observed the footage sent back by the probe until one of the Hole Ghosts ate it and pulled in all the cable line. Ray Stantz tried to save the probe and grabbed the end of the cable but was pulled in himself.