Smoke and fire: why we are not a smoke alarm

Terrestream's Sensirion SEN66 measures airborne particle mass (PM1, PM2.5, PM4, PM10) using a 660 nm laser scattering cell. It will see smoke. It will not save you from a fire. The detection latency is wrong, the response is wrong, and the alarm threshold is wrong. Every dwelling unit needs a UL 217-listed smoke alarm, properly placed per NFPA 72: one inside each sleeping room, one outside each sleeping area, one on every level including the basement, all interconnected so that one triggering wakes the rest.

The timing gap is the part most people underestimate. A UL 217 smoke alarm has to detect a developing fire within tens of seconds of visible smoke and produce an 85 dBA temporal-three pattern. A particulate sensor reports a rolling minute average. In a flaming kitchen-grease fire, PM2.5 will climb to several hundred μg/m³ within a minute, the dashboard will show it, you will see it on your phone if you happen to be looking, and by then the smoke detector at the ceiling has been screaming for fifty seconds. By the time the dashboard tells you anything, the alarm should already have told everyone in the house.

There is also the loudness gap. A smoke alarm is designed to wake a sleeping adult; a phone notification is not. National Fire Protection Association studies show that children in particular sleep through low-frequency tones and quiet electronics. The dashboard is silent by design. The CADR-driven PM2.5 notification may not even reach your phone if you have notifications off, and the audio cue (if you enabled it) is consumer-grade volume, not life-safety volume. None of this is a substitute for a 85 dBA T-3 horn six feet from your pillow.

Use the dashboard for what it is good at: confirming after the fact that a small kitchen fire actually did leave behind elevated PM, or showing that a candle is producing more soot than it appears to be, or quantifying how much wildfire smoke is making it indoors through closed windows. For "is my house on fire?" the answer comes from the ceiling, not the screen.