What Are the 3 Types of Smoke Alarms?

Ionization Smoke Alarms

• Ionization smoke alarms contain an ionization chamber that holds two electrically charged plates. Small amounts of radioactive material pass between the plates, creating a current. When smoke moves into the ionization chamber, it changes the current and causes the alarm to go off. This type of smoke alarm can detect fires that move quickly but do not create a lot of smoke. However, ionization smoke alarms tend to have more false alarms than other types.

Photoelectric Smoke Alarms

• Photoelectric smoke alarms contain an infrared light beam in the chamber. Under normal circumstances, the beam passes from one side of the chamber to the other without interruption. When smoke particles enter the chamber and block all or part of the beam, the alarm goes off. Whereas ionization alarms are better at detecting fast-moving fires, photoelectric alarms do a better job of detecting slow, smoldering fires, such as those created by a cigarette left on a couch.

Dual-Detection Alarms

• Dual-detection alarms are smoke alarms that combine the features of the ionization alarm and the photoelectric alarm. They are able to detect both slow, smoldering fires and fast-moving fires--those with large amounts of smoke and those with very little smoke. According to a 2009 study by Thomas Cleary for the National Institute of Standards and Technology, dual-detection alarms are able to detect smoke more quickly than an individual ionization or photoelectric alarm.

Reminders

• The NFPA suggests installing a smoke alarm outside of every bedroom and on every floor of the house. Because smoke rises, smoke alarms should be placed on the ceiling. They should not be installed near windows or vents, as a draft will affect their ability to work properly. Smoke alarms should not be painted. Change the batteries on the smoke alarm regularly. If the smoke alarm has been hard-wired into the home's electrical current, it should have a battery backup.