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

A biometric access control mechanism utilizes unique physical characteristics of an individual to grant or deny access. This means it relies on traits that are inherently tied to the person, such as fingerprints, iris recognition, facial recognition, or, as in this case, voiceprints.

The option of a door locked by a voiceprint identifier accurately represents biometric access control because it requires the user to provide their unique vocal characteristics to verify their identity. This method is inherently more secure than traditional access controls since it is difficult to replicate someone's unique voice.

In contrast, the other options represent different forms of access control. A badge reader, for instance, typically relies on a physical object rather than a unique physiological trait and can be lost or stolen. A copper key is a traditional mechanical lock-and-key method that is easy to duplicate. A fence with razor tape is a form of physical security but does not involve any biometric verification. Thus, the inclusion of a voiceprint identifier makes the indicated option the only one that fits the definition of biometric access control.