What devices are included in the category of Initiating Devices?

Initiating devices play a crucial role in fire alarm systems and are designed to detect conditions that indicate a fire or emergency, thereby initiatating an alarm response. The correct choice highlights that detectors, sensors, and pull boxes are the primary components recognized as initiating devices.

Detectors are instruments that identify smoke, heat, or other indicators of fire. Sensors may include those that detect changes in environmental conditions, such as temperature increases or gas emissions. Pull boxes, or manual pull stations, allow individuals to manually trigger the alarm system, making them an essential part of emergency response.

In contrast, the other options refer to devices that either provide alerts or contribute to the overall operation of the alarm system rather than initiating the alarm. Horns and strobes fall under notification appliances, which alert occupants to the presence of an emergency rather than detecting it. Exit signs serve a different function, guiding individuals to safety during an evacuation and do not contribute to detecting emergencies directly. Control panels and relays manage the operation of the system and respond to inputs from initiating devices but do not directly detect emergencies themselves.

Thus, the inclusion of detectors, sensors, and pull boxes defines the category of initiating devices clearly, aligning with their primary function in emergency response systems.