What type of device responds to physical stimuli such as heat or smoke?

A device that responds to physical stimuli such as heat or smoke is known as a detector. Detectors are specifically designed to sense changes in their environment and trigger an alert or response when certain conditions are met. For instance, heat detectors respond to temperature increases, which might indicate a fire, while smoke detectors identify the presence of smoke particles in the air, also signaling potential fire hazards.

In residential applications, detectors play a crucial role in safety, as they can activate alarms or notify a central system when they sense fire-related stimuli. This capability helps to protect occupants by providing early warning of dangerous situations.

Other options, while related to communication or feedback mechanisms, do not fulfill the same role as detectors. Transmitters and receivers are typically involved in sending and receiving signals, and a sensor can refer to devices that might gather data from the environment but do not inherently alarm or indicate critical conditions like heat or smoke. Therefore, the correct choice highlights the essential function of a detector in alerting individuals to life-threatening situations, such as fire.