Detector design changes when the test changes. The seventh edition of the UL 268 standard added two new fire tests that older alarms could not pass together: a polyurethane foam smouldering-and-flaming test, representing modern furniture, and a hamburger-cooking nuisance test that the alarm must not respond to. Passing both at once is contradictory for a single-channel device, because grease smoke and foam smoke overlap in particle size, so manufacturers moved to dual optical wavelengths, added heat or carbon monoxide channels, and put classification algorithms in the alarm. That is why alarms sold after the standard took effect behave differently in a kitchen from ones bought a decade earlier. The standard is named here as the origin of a sensor test, not as a code to obey; what matters is the general lesson that a test protocol written from real fire scenarios drives sensor architecture more than any physics breakthrough does. After this Concept you can explain why a modern alarm carries more than one sensing channel, and read a compliance claim as a statement about which fires the device was tested against.
Fire-detection standards (UL 217 for smoke alarms, UL 268 for smoke detectors) define product performance through sensitivity thresholds (percent obscuration/percent-per-foot) that must reliably dete…