How to install the cat's eye of security door?

There are two symmetrical slits on the cat's eye inside the door. Just aim something at the two slits and screw it off. Very convenient. It is correct to use a hole opener. Buy your favorite cat's eye first, then measure the inner diameter of the cat's eye, and then buy a hole opener. Pay attention to hold the electric drill tightly when opening holes, and don't scratch the paint of the security door.