Which of the following locks offers the highest level of security for exterior doors?

A deadbolt offers the highest level of security for exterior doors primarily due to its design and functionality. Unlike other types of locks, a deadbolt requires a key or a thumb turn to operate and features a solid metal bolt that extends deep into the door frame when locked, making it much more difficult for intruders to force open compared to locks that merely latch or hook.

Key in knob locks can be easily manipulated and are often considered less secure since they can be compromised with simple tools. Chain locks and sliding bolt locks also provide additional security but are relatively weak in comparison; chain locks can be easily bypassed if the door is not firmly shut, and sliding bolt locks are vulnerable if the door frame or mounting is weak.

The deadbolt's construction and its ability to resist forced entry strongly position it as the most effective option for enhancing the security of exterior doors, making it the preferred choice among security experts.