Most new prison keys have this feature, I think. It's some sort of retractable sheath of sorts that hides the profile of the teeth. And some high-security keys

Most new prison keys have this feature, I think. It's some sort of retractable sheath of sorts that hides the profile of the teeth. And some high-security keys don't have teeth at all. They have dimples of varying depth on the side of the key serving the same function instead. These don't jot out and are very hard to copy even photographically.