Which of the following is not an initiating device?

The McCulloh transmitter is primarily a signaling device rather than an initiating device. Initiating devices are components in a fire alarm system that detect a fire or a condition indicative of a fire and send a signal to the control panel to alert it of the situation.

Smoke detectors and water level switches both fall into this category as they actively respond to environmental changes: smoke detectors sense smoke particles in the air, while water level switches detect levels of liquid, often used to indicate whether sprinklers are functioning or a specific water presence is required. Electromechanical releasing devices can also activate upon detecting certain conditions, serving an initiating role as part of a broader system.

In contrast, the McCulloh transmitter serves as a method of communication within the fire alarm or suppression system but does not initiate an alarm itself based on environmental factors. Its function is more about sending signals after initiation has occurred, making it distinct from the initiating devices listed.