Most Mac models — and numerous peripherals, such as monitors, AirPort base stations, and external hard drives — include a small oval slot designed to accept a special lock at the end of a flexible steel cable. Kensington, a prominent manufacturer of computer accessories, holds the patent to this slot (making them the only company I'm aware of that has patented a hole), and some other companies, such as Targus, sell cables made for use with the Kensington Security Slot under license.
In most cases, the cables have a loop at one end. You wrap the cable around an immovable object, slide the lock end through the loop, and then attach it to your computer. (Some cables are designed to be bolted to a special bracket or attached in some other way.) The locks at the ends come in several styles. Some take flat keys, some take round keys, and others use a combination.
In addition to preventing someone from walking off with your equipment, the security cables serve a secondary purpose on most desktop Mac models. With the lock inserted, the case can't be opened, which means that internal components (hard drives, RAM, video cards, and the like) are also protected, and certain security risks that require an attacker to have access to the inside of the computer are reduced.
For more on preventing a hacker from having access to the inside of your Mac, see Chapter 6.
Security cables serve as a modest deterrent to casual theft. For example, they make sense for ...