Are All Detectors Created Equal? Odds are we've all got a little disc-shaped device in our homes that lets us rest easy - and no, we're not talking about your robot vacuum. If you guessed correctly, we're referring to the smoke alarms that tell us we'll be alerted in time should fire or fumes put us in danger. Even though they tend to look similar and are all built with the same purpose in mind, various smoke detectors work in several different ways. Detection technologies are tailored to numerous types of fires and smoke densities and it's best to be aware of these variations so you can make the smartest choices possible when protecting your home and family.

Most residential smoke alarms fall into one of two different categories: ionization and photoelectric. Let's look at the inner workings of each type to learn exactly which one will suit your needs.

IMPORTANT NOTE: While smoke and carbon monoxide often go hand in hand, CO can be emitted without the telltale smoke. To be safe, it's important to have both types of detectors in your home - or a combination detector that takes care of both in one device.

IONIZATION

Simple Explanation: The smoke that gets into the detectors blocks the electrical current, which sounds the alarm.

Long and Complicated Explanation: Equipped with ventilated ionization chambers that consist of two battery-charged metal plates (one positive, the other negative) and a trace amount of the element Americium-241 (first created in 1944, it acts as a source of radiation, named because it was created in the United States), these alarms work by ionizing air's nitrogen and oxygen atoms to detect harmful smoke in indoor environments.

Ionization takes place when the Americium-241 releases radiation in the form of alpha particles, which separate single electrons from the oxygen and nitrogen atoms within the chamber. These separated electrons - known as "free electrons" - have a negative charge, which draws them toward the positively charged battery plate. In the meantime, the positively charged, electron-deficient nitrogen and oxygen ions are drawn to the chamber's negatively charged plate.

As the electrons and ions move toward their respective plates, the device's electronics are aware of the slight electrical current that their movement produces. When smoke particles enter an ionization chamber, they attach themselves to and absorb the ions, neutralizing them and disrupting the electrical current. The detector senses the change in current and an alarm is sounded.

Contrary to the images of danger that radioactive elements and radiation can bring, ionization alarms are very safe. The amount of americium-241 they contain is extremely minute (less than one milligram). The element would have to be inhaled or ingested to do any harm. The radiation produced by americium-241 is made up almost exclusively of alpha rays, which are unable to penetrate a sheet of paper, much less the detector's plastic casing.

A common fire safety measure in many homes, ionization alarms are generally very cost effective, and are particularly good at detecting very small amounts of smoke, as would occur with a quick-flaring fire. We recommend Kidde's Micro Ionization and Wireless Interconnectable Ionization alarms.

PHOTOELECTRIC

Simple Explanation: When smoke blocks the light receptors of this type of unit, an alarm sounds.

Long and Complicated Explanation: Sometimes referred to as optical detectors, photoelectric smoke alarms use light-sensing technology to identify the noxious fumes. Typically, this system is made up of three main elements: a light source (incandescent or LED), a lens (which focuses light from the source we just mentioned into a concentrated beam) and a photo-sensor, which is usually placed at a 90° angle to the light beam.

If there's no smoke present in the air, the beam shines straight ahead, parallel to the sensor's surface. However, as soon as offensive particles drift into the detector, they disrupt the beam, scattering light in multiple directions, including toward the photo sensor. This automatically triggers an alarm as soon as it detects the stray light waves.

Photoelectric alarms are ideal for detecting slower-burning fires that produce a lot of smoke. They're less likely than ionization detectors to trigger a false alarm from kitchen and bathroom steam.

COMBINATION IONIZATION/PHOTOELECTRIC

The most complete way to protect your house is by using an alarm that utilizes both methods of detection. Combination smoke detectors eliminate the guesswork involved in choosing the best type of device for each area of your home because they've got it all covered: ionization detection for sudden, low smoke flame-ups and photoelectric sensors for smoky, slow-burning fires.