Door cylinders, commonly found in pin tumbler locks, operate using a series of pins of varying lengths within a cylinder. When the correct key is inserted, it aligns the pins at the shear line, allowing the cylinder to rotate freely. Incorrect keys misalign the pins, obstructing rotation. Modern cylinders may include security features like sidebars or magnetic pins for added protection against picking or bumping.

Additionally, some cylinders utilize electronic components for keyless entry systems, further enhancing security. Overall, door cylinders provide a reliable and versatile mechanism for securing doors in residential, commercial, and industrial settings.