Ectoplasmic Glasses are a type of equipment dedicated to detection of supernatural entities.
During Christmas Eve, Egon Spengler wore a pair of Ectoplasmic Glasses while on route to meet with Peter Venkman and Ray Stantz at the penthouse of Woodrow Wainwright Fraser III. The ionisation array held up very well, but it took Egon an extra 18 minutes and 42 second and two minor traffic accidents to make it to his destination. Thus, it appears they are best worn only during a bust in progress. When the Ghost of Christmas Past arrived, Egon instantly detected her with the device.