What device is used to detect fire and send a signal to the control unit?

The device that detects fire and sends a signal to the control unit is typically referred to as an initiating device. Initiating devices are essential components in fire alarm systems, designed specifically to sense the presence of smoke, heat, or flame and provide the critical information needed to trigger an alarm response.

When a fire occurs, the initiating device detects specific parameters indicative of a fire situation and sends a signal to the control unit, which then activates alarms and notifications. This action is vital for ensuring safety, as it alerts occupants and emergency personnel of fire situations promptly.

In contrast, while sensors are indeed part of many initiating devices, not all sensors are dedicated to initiating alarm responses. Indicating devices, on the other hand, are meant for signaling an alarm state rather than initiating it. Vibration devices do not typically serve a role in fire detection systems, as they are not designed to sense fire conditions or trigger alarms. Thus, the focus on the function of initiating devices highlights their crucial role in fire alarm systems, making them the correct answer.