Which of the following accurately describes a manual access control system?

A manual access control system is characterized by its simplicity and the direct involvement of individuals in the entry process. The correct choice of a stand-alone system using a 3- or 4-digit code exemplifies this concept, as it does not rely on complex integration or electronic verification methods that involve multiple components.

In this context, a manual access control system typically allows for straightforward entry based on memorable codes that users must input directly, which aligns with the idea of manual operation. Such systems are often deployed in smaller settings where the volume of individuals needing access is manageable, and the requirement for high levels of security is less critical compared to more advanced systems.

Other options describe systems that incorporate more advanced technology and automation. For instance, biometric scans, centralized networks, and identity badges with chips imply integrated systems that automate access based on technological inputs and connectivity, making them unsuitable for the description of a manual system.