What does a photoelectric smoke detector primarily detect?

A photoelectric smoke detector primarily detects slow-smoldering fires due to its design and operating principle. It utilizes a light source and a sensor to detect smoke particles in the air. When smoke enters the detector, it scatters the light beam, alerting the system and triggering the alarm.

Slow-smoldering fires, which often produce large amounts of smoke and fewer flames initially, are more effectively identified by this type of detector. This makes photoelectric detectors particularly useful in areas where such fires might occur, such as in the presence of materials like textiles or furniture that burn slowly and create dense smoke.

In contrast, fast-burning fires, high heat, and carbon monoxide are detected more effectively by other types of detectors. Fast-burning fires produce flames that may not generate enough smoke for a photoelectric detector to respond quickly. High heat detection is primarily the domain of heat detectors, while carbon monoxide detection is associated with specific CO detectors. Hence, the primary purpose and effectiveness of photoelectric smoke detectors in detecting slow-smoldering fires underscore the chosen answer's accuracy.