What do photoelectric, projected beam type, and reflective beam type smoke detectors have in common?

Photoelectric, projected beam type, and reflective beam type smoke detectors share a common operational principle: they utilize a light source to detect smoke.

In each of these devices, the presence of smoke in the air disrupts the light path or the light intensity in some manner, triggering an alarm. Photoelectric detectors work by sending a light beam through a sensing chamber where smoke can scatter the light, signaling the presence of smoke. Projected beam detectors operate similarly but often cover larger areas by transmitting beams over longer distances; again, smoke particles interfere with the beam. Reflective beam detectors use a light source and a reflector positioned at a distance, where smoke interference can also signal an alarm when the light beam is obstructed or scattered.

This reliance on light detection is what links all three types of smoke detectors together, emphasizing their fundamental purpose: identifying smoke particles in the environment to ensure safety. The other options do not uniformly apply to all three types; for instance, while some may be battery-operated, not all are, and they primarily detect smoke rather than heat changes, and they are not limited to commercial buildings as they can also be used in residential settings.