Most folks know there are a two of different types of Smoke Detectors available in your local hardware store:


This type of detector contains a light emitter, most likely an infrared LED, a lens that turns the source into a beam, and a light sensor that sits at an angle across from the beam. During normal conditions, the light in the beam shines in front of the detector (nearly perpendicular). When smoke enters the chamber, light bounces off the smoke particles and into the photo sensor, triggering the alarm.

Optical sensors are good at detecting smoldering fires, which produce a lot of smoke, but apparently do not react as quickly to rapidly building fires – they still provide adequate warning, however.


Second are the Ionizing smoke detectors. These contain a small amount of a Americium-241, a radioactive isotope found in nuclear waste with a half-life of 432 years. As the 241Am decays, “The radiation passes through an ionization chamber, an air-filled space between two electrodes, and permits a small, constant current between the electrodes. Any smoke that enters the chamber absorbs the alpha particles, which reduces the ionization and interrupts this current, setting off the alarm.”

It should be noted that 99% of the radiation emitted is Alpha radiation which due to it’s low penetrative power, is stopped by the plastic housing of the detector.

Ionizing smoke detectors can detect smaller particles than the Photo-detection types, but also are more prone to false alarms (leading people to turn them off)

Dual Function

For what it’s worth, you’re best bet is to get a detector that uses both type of technology to tell you that you burned dinner.

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