#UL 217

1 article.

Two round white smoke alarms mounted side by side on a hallway ceiling at night, with grey smoke drifting toward them from a doorway lit by a faint orange glow and a moonlit window at the right

Fire Safety Engineering

Ionization or Photoelectric Smoke Alarm? Why Experts Split

Ionization alarms beat a photoelectric smoke alarm by seconds in flaming fires, then lose by 30 minutes in smoldering ones. Here is why experts still split.

September 25, 2026 · 19 min read