What is a defined area within the protected premises known as?

The correct choice is referred to as "Zone." In the context of security systems and fire alarms, a zone typically defines a specific area within a protected premises that can be monitored or managed using detection devices. This concept allows for effective management, identification, and response to security breaches or alarms, as each zone can relate to a specific part of a building, such as different floors, rooms, or sections.

By using zones, system operators can quickly determine the exact location of an alarm or security issue, facilitating a directed response. Each zone can have its own set of devices or alarms linked to it, allowing for tailored security measures and more effective monitoring.

The other terms may refer to smaller sections or divisions within a broader context but do not specifically imply the standardized definition or operational function that "zone" carries within security and alarm systems. A boundary might suggest limits in a more physical sense, while sections and fields are much less specific when it comes to defined operational areas in this context.