Which of the following is explicitly NOT a requirement of a secure telephone system in a SCIF?

A secure telephone system within a Sensitive Compartmented Information Facility (SCIF) has several essential requirements aimed at protecting sensitive information and ensuring its security during communications. Among these requirements, the encryption of conversations, operation within a controlled frequency range, and prevention of eavesdropping are critical elements for safeguarding communications.

The correct choice highlights that the detection of unauthorized human entry into a SCIF is not an explicit requirement of a secure telephone system itself. While ensuring physical security, including monitoring for unauthorized access, is crucial for a SCIF overall, the secure telephone system's specific mandate focuses on the integrity and confidentiality of the communications it facilitates rather than the monitoring of the facility's perimeter or the detection of intrusions.

Therefore, while physical security is vital in a SCIF, it falls under general security measures for the facility as a whole rather than a specific requirement for the telephone system. This delineation clarifies the primary function of the secure telephone system, which is to ensure that conversations remain confidential and protected from potential interception.