Protecting businesses and more importantly the people who work and spend time in facilities against intrusions is an important and necessary activity. We usually think of larger organizations, universities, hospitals, government facilities, banks etc as needing protection systems. In my experience, smaller entities (under 1000) rarely have the time, motivation, money, or energy to draw on to implement elaborate protections. Many do have rudimentary preventions like badge access, redundant information backups, and password protections. Some use security cameras and might have a small backup power supply like a generator.
Depending on the nature of the business and the historical incidents (of intrusions), an organization may be more or less compelled to consider protection against intrusions in their IS Continuity Plan[example].
I think there is a strong relationship between protection and continuity, especially at the enterprise level. I’m a fan of strategic planning. As such, when considering continuity planning, it makes sense to me that the security protection systems is part of an overall continuity planning process. There may be times or situations when a security system is stand-alone due to the size or complexity of a facility. In such cases, the IT continuity plan would certainly contain a ‘chapter’ on how the IT protection is being handled and how that set of methods interfaces with the overall security infrastructure.
Often, the IT function can implement its own protection system (including data, cyber, physical, logical) without the need for integration into the larger company scheme.
However, given the choice, I am in favor of an integrated protection system. The reason for this is that trade-offs and comprises, cost-benefit analysis, and budget constraints can possibly be optimized more efficiently when a more global perspective is considered by the organization. Also, sometimes one type of prevention or mitigation can easily include wider scope without much additional cost. Examples might include physical facility access/egress installations, fire protection systems, or building design and layouts.