What is the primary purpose of using a projected-beam type detector?

The primary purpose of using a projected-beam type detector is to protect large open spaces. These detectors work by projecting a beam of light across an area and monitoring for any interruptions in that beam, which could indicate the presence of smoke or other obstructions. Their design is particularly suited for large areas such as warehouses, atriums, or auditoriums where traditional point detectors might not effectively cover the space or may not be efficient in detecting smoke quickly.

In contrast, other options focus on different detection methods or purposes. Detecting heat is more aligned with heat detectors rather than projected-beam types, which are primarily used for smoke detection. Monitoring air quality is a function typically associated with specific air quality sensors, rather than the beam interruption technology used in these smoke detectors. Detecting smoke from small sources is more effectively done with point-type smoke detectors that can catch smoke from specific locations, whereas a projected-beam type is not ideal for this purpose due to its design optimized for larger areas.