Which of the following is the BEST example of a physical security barrier?

A firewall is a network security device or software that filters traffic between network segments; it provides no physical access barrier.

A Cypherlock is a physical access control device - typically a keypad or combination lock mounted on a door - that prevents unauthorized physical entry into a secured area. It is a hardware barrier that stops physical intrusion, satisfying the definition of a physical security control.

Strong passwords are a logical authentication control that protects digital accounts and systems but do not restrict physical access to a location.

BitLocker is a Windows full-disk encryption feature that protects data at rest; it is a software-based security control, not a physical barrier.