If control units cannot be located in the protected premises, what is an alternative for protecting their enclosures?

The correct choice emphasizes the importance of supervision as a viable alternative when control units cannot be located on the premises they are intended to protect. Providing supervision to annunciate tampering means implementing a system where personnel are actively monitoring the area and its access points. This proactive approach allows for immediate response to any unauthorized access or potential tampering with the enclosures that protect vital control units. The presence of supervising individuals can act as a deterrent to trespassers and can ensure that any suspicious activity is quickly addressed.

In contrast, while using stronger materials or locking mechanisms might fortify the enclosures, these methods alone may not respond to real-time threats. They could be compromised without supervision, making them less effective. Regular training of personnel is beneficial, but without the immediate observation that supervision provides, trained personnel won't be able to monitor and respond quickly to actions occurring in the vicinity of the control units. Thus, supervision serves as a dynamic safeguard to enhance the security of the enclosures effectively.