What are manual initiating devices limited to?

Manual initiating devices are specifically designed to require human intervention to activate a fire alarm system. In this context, manual fire alarm boxes are prime examples of such devices as they enable individuals to alert others and activate the fire alarm system in the event of a fire. These boxes must be intentionally pulled or pressed to initiate an alarm, reflecting the characteristic of manual operation.

Electronic valve supervisory devices also complement the function of manual initiating devices by monitoring the status of fire protection systems and ensuring that valves are in the correct position for optimal performance, although they may not directly initiate a fire alarm response. These components are vital to the overall functionality of fire safety systems, emphasizing the role of human action in initiating alerts or responses to a fire incident.

In contrast, the other options include devices that automatically detect smoke, heat, gas, or carbon monoxide without necessitating any manual action, which does not fit the definition of manual initiating devices.