Features

• Positive and negative charges of ions create a measurable current.battery image by Hao Wang from Fotolia.com
  
  Ionization smoke detectors are typically built with four major components. There is an aluminum ionization chamber containing a mildly radioactive material, usually the element americium. Americium has a half-life of 432 years, meaning it doesn't need to be replaced often.
  
  The second feature is a pair of plates, one positively charged, and one negatively charged.
  
  Lastly, there is a sensor.
  
  

Function

• The reason that radioactive particles are used is that they "ionize" the air in the ionization chamber. This means that the atoms of air, which are oxygen and nitrogen atoms, get their electrons detached by the presence of the radiation. The result is a batch of ions that are either positively charged or negatively charged.
  
  This group of ions is then "herded" towards one of the charged plates. The positives flock to the negatively charged plate, and the negatives fly to the positively charged plate. The result is a measurable current of ion-flow. As long as nothing disrupts that flow, everything is fine.
  
  

Effects

• Ionizing smoke alarms make use of mild radioative particles.radioactive image by red2000 from Fotolia.com
  
  This harmony is not to last when smoke is in the air. When even a small particle of smoke enters the ionization chamber, there is an instant subatomic reaction The predictable current is disrupted, because the smoke particles bind to the ion population, reducing overall ionization in the chamber. This disruption is promptly noted by the sensor, and the alarm goes off.
  
  

Radiation

• Americium is, as noted, very weak and can be easily contained in the detector with no danger of leakage. The specific kind of radiation is alpha radiation, which is selected because it has poor penetrating power, unlike other kinds of radiation which easily penetrate most substances.
  
  However, americium is still radioactive. While it poses no danger while contained, a damaged or willfully ruptured detector can potentially expose people to radiation.
  
  

Warning

• Studies have shown that dual alarms work better than single alarms.Smoke image by peter Hires Images from Fotolia.com
  
  Ionizing smoke alarms have been criticized at both ends of the debating spectrum. Some have been noted for triggering false positives, due to malfunctioning sensors or something wrong with the innards of the detector itself that cause disruption to the current without the presence of smoke being needed.
  
  Another set of critiques come from a series of tests that show dual alarms are more effective than ionization alarms or photoelectric alarms by themselves.