The 8 Best Smoke Alarms
Two Ways To See The Smoke
That increase in light hitting the sensor sets off the alarm.
You'd have to break open the chamber and rub the Americuim-241 all over your eyeballs to get a negative effect.
The image you're looking at is a rough peek at the layout inside of an ionization smoke detector. These, along with photoelectric smoke detectors are your best bets for detecting a fire in your home, but each one has its advantage over the other.
In the ionizing smoke detector, you're installing a small radioactive device in your home. But don't worry; your pregnant cat isn't about to give birth to a three headed kitten who speaks Spanish. It's not that kind of radiation.
Within the housing of an ionizing smoke detector is a small amount of Americium-241, a radioactive isotope that emits alpha particles throughout a plastic chamber.
The good news here as far as your safety goes is that alpha particles are pretty weak, too weak, in fact, to penetrate the plastic of the chamber, and weaker still when exposed to a large area. You'd have to break open the chamber and rub the Americuim-241 all over your eyeballs to get a negative effect.
Anyway, as the material decays its alpha particles ionize the oxygen and nitrogen in the air, the resulting positively charged atoms and negatively charged electrons of which are drawn to two leads in the compartment, each of which is charged either negatively or positively.
That creates a nice little current. When smoke, or steam, or excessive heat enters the chamber, it interferes with the ionization process, reducing the current, which sets off the alarm. That makes ionization smoke detectors ideal for detecting flash fires, kitchen fires, and any other fire that produces a lot of heat, without necessarily producing a lot of smoke.
Photoelectric sensors, on the other hand, require no radioactive materials. While that doesn't make a real difference in their safety considering the relative safety of Americium-241, it does mean that they don't require any special disposal the way ionizers do.
Instead of relying on ionization, photoelectric smoke detectors use LEDs to send a beam of light across the top of a T-shaped tube. At the bottom of the T is a photo cell that detects the base amount of light leaking down the stem of the T.
When smoke enters that chamber, its particles reflect a lot more light down the stem and onto the photo cell. That increase in light hitting the sensor sets off the alarm.
A design like this makes a photoelectric smoke detector ideal for picking up slow smoldering fires like the ones started by cigarettes or the one burning inside you whenever you think of your in-laws.
Fire In The Hole!
So, you know how each of the two types of smoke alarms works, but that might not yet have cleared up the burning question: which kind should you buy?
I'll make it easy for you. You actually need both.
I'm not saying that you absolutely have to have both kinds of smoke detectors at every detection point in your home, although that would be the safest way to set them up.
Since ionization smoke detectors are best suited for picking up big, flashy fires, the kitchen seems like an obvious choice for one of those.
At the very least, take a look around your home to evaluate the different types of fires that are likely to spark up in each, and determine the best kind of alarm for that area.
Since ionization smoke detectors are best suited for picking up big, flashy fires, the kitchen seems like an obvious choice for one of those. Electrical fires can get high and hot very fast as well, especially if they start in a wall with flammable insulation, so anywhere that you're challenging the electrical load of a circuit (by your entertainment center, for example) would be a good place for an ionizer.
You'll want to place your photoelectric sensors anywhere a smoldering fire would take place, as well as anywhere people might be sleeping. Since the majority of fire-related deaths result from smoke inhalation, the extra time it'd take for an ionization detector to wake you up during a slow, smokey, smoldering fire might cost you your life.
The One Time Smoking Saved Lives
The story goes that a Swiss physicist named Walter Jaeger was working hard on a device that could detect poisonous gasses.
This was back in the late 1930s, after gaseous chemical warfare had been unleashed in WWI.
His idea was simple: he thought that gas particles would disrupt the ionization process of a radioactive isotope in an airy chamber, altering the current of two leads. Sound familiar?
Well, as his experiments failed to produce an alarm, Jaeger sat down and sadly lit a cigarette. You can guess what happened next. The alarm went off, and Mr. Jaeger realized that he had accidentally invented the modern smoke detector.
The early 70s saw both the commercialization of the ionization smoke detector and the introduction of the first optical photoelectric smoke detectors, both of which dominate the market to this day.