Voice recognition is a form of biometric identification used for physical security. This method analyzes the unique physiological and behavioral characteristics of an individual's voice, such as pitch, tone, and cadence, to verify their identity. It is implemented in physical access control systems to grant or deny entry to secure facilities, like data centers. Unlike other options, voice provides a distinct, measurable, and verifiable trait specific to an individual for identification purposes.

B. Expression: Facial expressions are temporary behavioral states, not a reliable or unique physiological trait for primary identification in security systems.

C. Sound: This term is too broad and non-specific. While voice is a type of sound, "sound" itself is not a defined identification method.

D. Batch ID: A Batch ID is an identifier for a group of products in manufacturing or logistics; it is entirely unrelated to human identification.

1. Jain, A. K., Ross, A., & Prabhakar, S. (2004). An introduction to biometric recognition. IEEE Transactions on Circuits and Systems for Video Technology, 14(1), 4-20. In Table I on page 5, "Voice" is explicitly listed as a common biometric identifier used for authentication, alongside other modalities like fingerprint and face. (DOI: https://doi.org/10.1109/TCSVT.2003.818349)

2. Stallings, W., & Brown, L. (2018). Computer Security: Principles and Practice (4th ed.). Pearson. Chapter 15, "Physical and Infrastructure Security," Section 15.2, discusses physical access control, identifying biometrics as a key authentication mechanism. It lists voice patterns as a static physiological biometric used for identity verification.

3. ISO/IEC 27002:2022, Information security, cybersecurity and privacy protection — Information security controls. Control 7.2 "Physical entry" outlines the objective to prevent unauthorized physical access. The guidance notes that entry controls for secure areas can be based on authentication mechanisms, which include biometrics (e.g., voice, fingerprint).