Douglas Krantz - Technical Writer - Describing How It Works

Don't Smoke Alarms Detect Smoke?

You've heard that smoke alarms detect smoke from a fire. What they actually detect is particles in the air and call the particles smoke. The particles can be cooking smoke, shower steam, cleaning dust. . . and even particles in real smoke from a real fire.

Looking closely at smoke one can see particles make up the visible part of the smoke
Smoke that we can see is made up of particles in the air. Smoke alarms see these particles and declare that they must be smoke. Having made the smoke delaration, smoke alarms sound the alarm.

By Douglas Krantz

A smoke alarm isn't really a smoke alarm at all; a smoke alarm is a particles-in-the-air alarm. When a smoke alarm detects particles in the air, it calls the particles smoke, and then sounds the alarm.


True smoke is usually solid particles of unburnt fire fuel and liquid particles of unburnt fire fuel. Gases and other components are also present, but for all practical purposes, a smoke alarm only detects the particles.

Cooking Smoke

When cooking, small particles (sometimes the particles are so small they can't even be seen) can be detected. The smoke alarm (which really isn't very smart) can't tell these particles from the smoke of a grease fire. For people's safety, the smoke alarm sounds the alarm.

Shower Steam

When a hot shower is taken, the steam particles in the air look to the smoke alarm like any other particles in the air. For people's safety, the smoke alarm sounds the alarm.


When there's a fire, the smoke from the fire finds its way to the smoke alarm. At this point, the smoke alarm detects particles in the air. For people's safety, the smoke alarm sounds the alarm.

Particles in the Air

Smoke alarms are there for people's safety. However, like anything else, smoke alarms have limits to what it can do. Smoke alarms can't tell the composition of particles, and they can't tell what caused the particles to be in the air in the first place.

Smoke alarms can only tell that there are particles in the air, and then sound the alarm.
Life Safety
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