Which of the following is an example of a biometric access control mechanism?

A biometric access control mechanism is designed to verify an individual's identity through unique physical or behavioral traits. The use of a voiceprint identifier falls squarely within this category, as it relies on the unique characteristics of a person's voice to grant or deny access. This method analyzes various attributes of a person's speech, such as pitch, tone, and frequency patterns, to create a biometric template. When someone attempts to access a secure area, their voice is compared against this template to verify their identity, ensuring that only authorized individuals can gain entry.

In contrast, the other options represent different types of access control mechanisms that do not utilize biometric data. A badge reader, for example, functions by scanning a physical card or badge presented by a user, which is not a biometric authentication method. Similarly, a copper key is a traditional locking mechanism reliant on a physical key, and a fence with razor tape serves as a physical barrier for protection rather than an identification or access verification process. Hence, the voiceprint identifier is the only choice that exemplifies the application of biometric technology in access control.