What is a characteristic feature of automatic initiation devices?

A characteristic feature of automatic initiation devices is that they automatically trigger alarms without human involvement. This capability is fundamental to their design and function, allowing them to respond promptly to certain conditions or stimuli—such as smoke, heat, or gas release—without the need for a person to manually activate them. This automation enhances the overall safety and responsiveness of fire protection systems, ensuring that alarms sound or systems engage immediately when necessary, ultimately reducing response times and potentially saving lives.

In contrast, the other options depict characteristics that do not align with the essence of automatic initiation devices. For instance, requiring manual intervention for activation goes against the automated nature of these devices. Similarly, utilizing human input for routine checks implies a level of interaction that is not characteristic of fully automatic systems, which are designed to function independently. Lastly, responding only to visual cues does not encompass the full range of stimuli that automatic initiation devices can detect, such as heat or smoke, thereby limiting their operational scope.