What component is present in a photoelectric smoke detector?

A photoelectric smoke detector operates based on a specific principle that involves a photoelectric cell. This component is essential for the detector's function, as it detects smoke particles in the air. When smoke enters the detector's sensing chamber, it disrupts a beam of light emitted by the photoelectric cell, causing a reduction in light intensity that triggers the alarm.

The photoelectric cell is crucial because it can identify smoldering fires more effectively than other types of smoke detectors that rely on ionization. This makes photoelectric detectors particularly useful in environments where slow-smoldering fires might occur, as they can provide earlier warning compared to other methods.

In contrast, other components listed, such as a pressure relief valve, a gas detection unit, and a heat sensor, do not serve the function of detecting smoke or the presence of combustion byproducts in the same way. Therefore, the presence of a photoelectric cell is what defines the functioning of a photoelectric smoke detector.