Key shells normally break out of normal wear and tear, but also break when dropped and it hits a hard surface. Many remote car key users have learned that plastic becomes weak with age. So it is very possible that you can experience a broken or cracked car key shell even when it didn’t hit a hard surface. Every time you start your car, the action of twisting the key within the ignition also stresses the section where the key blade meets the plastic shell. So even with specially formulated plastics, cracks will still happen and when the repeated action of twisting the key within the lock or ignition persists, it will end in a broken key shell.