While it has been super rare to experience any customer complaints, it is recommended to test a sample of our car door magnet on the specific vehicle you will be using the car door magnets with, as some cars have aluminum doors and magnets will not stick. Even easier, if you are unsure if your vehicle is magnet receptive, grab any ordinary refrigerator magnet and test the area where you want to place a magnetic sign. If it sticks, you are good to go!