If smoke is coming into the area where this breaking apart is happening, it will block the charged particles from moving, reducing the current. A newer kind of smoke detector is based on the photoelectric effect. Engineers figured out how to tune a light source in a way that is sensitive to smoke. The light can be shining and you get current. If it is tuned correctly, you can interpret that change in current as the presence of smoke.
And again, you can get false positives because organic compounds often absorb infrared light really well. The photoelectric ones probably are more power intensive. So your battery life span may not be as good. But, hey, you should be changing it every six months anyway. Festival of Social Science — Aberdeen, Aberdeenshire.
When the number of particles entering the chamber is enough to reduce that current below a certain amount, the device will register those particles as smoke and the alarm will sound. And about that radioactive material? Most of its radiation is blocked inside the device, and even then, the radiation levels in the device are much lower than the natural background radiation to which we are exposed every day.
The other type of commonly used detection technology is called photoelectric. This technology works by detecting light that is reflected off particles from a light beam inside the sensing chamber. When no particles are present in the sensing chamber, the light from the beam does not strike the light detector, indicating all clear.
When there are particles present and the amount of light registered by the light detector reaches a certain threshold level, the alarm sounds. Ionization-based alarms tend to detect small black soot particles from flaming fires more quickly because they are produced in greater numbers and take away more current from between the plates. Photoelectric detectors tend to be more sensitive to particles that are larger in size and white or light-colored, and thus more reflective, like those emitted by smoldering fires.
The NFPA advises that people have both ionization and photoelectric units in their homes. And dual-sensor alarms that combine both technologies are also available. As important as smoke alarms are for protecting your family and your property, many times they can be a nuisance. When smoke enters the ionization chamber, it disrupts this current -- the smoke particles attach to the ions and neutralize them. The smoke detector senses the drop in current between the plates and sets off the horn.
Speaking of alarms, whenever the words "nuclear radiation" are used an alarm goes off in many people's minds. The amount of radiation in a smoke detector is extremely small. It is also predominantly alpha radiation. Alpha radiation cannot penetrate a sheet of paper, and it is blocked by several centimeters of air.
The americium in the smoke detector could only pose a danger if you were to inhale it. Therefore, you do not want to be playing with the americium in a smoke detector, poking at it, or disturbing it in any way, because you don't want it to become airborne.
See How Nuclear Radiation Works for further details. When you take off the cover, you find that a smoke detector is pretty simple. This one consists of a printed circuit board see the article Inside a Remote Control for an explanation of printed circuit boards , an ionization chamber the silver cylinder toward the top right in the following picture and an electronic horn the brass cylinder toward the bottom right in the following picture :.
The ionization chamber is an aluminum can containing the ionization source. You can see that the can has slots in it to allow air flow. The can itself acts as the negative plate of the ionization chamber.
Underneath the can is a ceramic holder that contains the positive plate of the ionization chamber. For more information on smoke detectors and related topics, check out the links on the next page. Sign up for our Newsletter! Mobile Newsletter banner close. Mobile Newsletter chat close. Mobile Newsletter chat dots. Mobile Newsletter chat avatar. Mobile Newsletter chat subscribe. Home Improvement. Home DIY. Household Safety.
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