The RoadGuard tool is effective only against clear and tinted tempered glass. Tempered glass is commonly used in rear and side car windows. The RoadGuard tool does NOT work on laminated glass. Laminated windows which are typically used for windshields can also be found on some car models. To check to see what your side windows are made of, locate the sticker on your side windows to see if it is designated as “Tempered” glass.