What is a key element in the functionality of water level supervisory signal initiating devices?

The correct answer emphasizes that water level supervisory signal initiating devices are capable of initiating signals regardless of whether they are in pressurized or non-pressurized settings. This versatility is crucial for their functionality in various applications where water levels need monitoring, including fire protection systems. Unlike options that suggest limitations—such as only monitoring water levels, being unaffected by temperature changes, or requiring manual checks—this choice highlights the operational adaptability of the devices. Effective water level supervisory systems can trigger necessary responses under varying conditions, thereby ensuring safety and reliability in fire alarm systems.