Mechanical door locks regularly remain even after electronic access control is added. Indeed, most are designed to work with what is already hung on the door. However, what happens when a lock needs to be replaced or changed? Understanding the basics of selecting and installing door locks is valuable for every designer, installer, or end user to know. In this note, we take a look at the basic types of locking hardware, which types of openings use them, and provide a general overview of how to install them.