Car alarms and smoke alarms: tradeoff between sensitivity and specificity (2012)

A trope of this style is “{interesting half story} but more on that later”.

I don’t think it is a big deal and I don’t see much self promotion here other than vanilla blogging, i.e. sounds like this person is knowledgeable let’s check their bio.

There's been quite a bit of research done, generally easy to find if you look, that talks about the difference and tests them, but the short summary:

- Ionization type sensors detect the products of fast flaming combustion and "things cooking in the kitchen." Your oven, if a bit dirty, will reliably trip an ionization type. They are quick on the draw for this. The downside is that they're very, very poor at detecting the sort of slow, smoking, smoldering combustion that is associated with house fires that kill people in the middle of the night.

- The photoelectric type is very good at detecting smoke in the air - but it isn't nearly as prone to false triggers on ovens, a burner burning some spills off, etc.

They've been A/B tested in a wide variety of conditions, and in some cases, the ionization type is a bit quicker. In other cases, the ionization type is slower, by time ranges north of half an hour - I've seen some test reports where there was a 45 minute gap, while the photoelectric type was going off, before the ionization type fired!

In general, "rapid fires during the day" are somewhat destructive to property, but rarely kill people. If your kitchen catches on fire while you're cooking, it may burn the house down, but generally people are able to get out.

The fires that kill people are "slow starting fires during the night" - the sort that smolder for potentially hours, often slowly filling the house with toxic smoke, before actually bursting into open flames. On this sort of fire, the photoelectric type will fire long, long before the ionization type - in some cases, they get around to alarming quite literally "after the occupants are dead from the smoke."

Using smoke alarms as a way to talk about monitoring systems is nice, but in terms of actual smoke detectors, get at least a few photoelectric sorts in the main areas of your home.

Do not get the "combined sensor" sort, since these tend to be and-gated and the worst of both worlds.

Edited to add some resources:

A presentation on the matter from a while back by one of the experts in this field: https://wahigroup.com/Resources/Documents/Ion%20vs%20Photo%2...

Another paper: https://www.semanticscholar.org/paper/Detection-of-Smoke-%3A...

> Full-scale fire tests are carried out to study the effectiveness of the various types of smoke detectors to provide an early warning of a fire. Both optical smoke detectors and ionization smoke detectors have been used. Alarm times are related to human tenability limits for toxic effects, visibility loss and heat stress. During smouldering fires it is only the optical detectors that provide satisfactory safety. With flaming fires the ionization detectors react before the optical ones. If a fire were started by a glowing cigarette, optical detectors are generally recommended. If not, the response time with these two types of detectors are so close that it is only in extreme cases that this difference between optical and ionization detectors would be critical in saving lives.

In any case, not all signals are the same. Most systems have a lot of components interacting and what turns to be dangerous is usually a combination of factors, but in the end, what defines that it was or not is that the system is doing what it should. You can put some guessing thresholds, but you must contrast it with that the system works.

And they should be actionable too, at least for alerts instead of slow day notifications, or metrics giving context to perceived problems that could take out the guessing from the thresholds.