There are two main types of smoke alarms, “Ionization” and “Photoelectric”. Ionization smoke alarms sound quicker in an open “flaming” fire while Photoelectric alarms sound quicker in a “smoldering” fire.
I saw a local hardware store had a combination Ionization and Photoelectric smoke alarm for $23. These are sometimes called “smoke and fire” or “dual sensor” alarms. I bought a Photoelectric alarm for $13 and put it next to the two year old Ionization one. Thankfully there was no fire at my house and my son and his pets are ok.
Many experts recommend changing smoke alarms every 10 years as the sensors do wear out. When you push the test button on a smoke alarm and hear a beep, it does not necessary mean the sensor is working, it can just mean the battery has sufficient voltage.
So don’t skimp on smoke alarms! Replace older ones with dual sensor, “smoke and fire” alarms. If you have an attached garage or fuel burning appliances be sure to install Carbon Monoxide alarms in or near bedrooms.
I have had the below information in my inspection reports for years and now truly realize that “for the best protection both kinds of smoke alarms are recommend.”
Smoke alarms are credited with saving many lives over the years. There are two main types of smoke alarms. Photoelectric smoke detectors contain a light source and a light-sensitive electric cell.
Smoke entering the detector deflects light onto the light-sensitive cell, triggering an alarm. Ionizing sensors contain a small amount of americium-241, a radioactive material. It is used to set up a small
electrical current between two metal plates which, when disrupted by smoke entering the chamber, sounds the alarm. In recent years, several national groups have come out with advisories saying that for the best protection, both kinds are recommended.
The National Institute for Standards and Technology tested the two technologies in 2004 and found that ionization smoke detectors sounded in fast, flaming fires an average of 50 seconds earlier than photoelectric detectors. NIST also found that photoelectrics sounded their alarms, on average, 30 minutes earlier than ionization detectors in smoldering fire. Testing by UL last year supported results obtained by the National Institute of Standards and Technology in 2004 that showed ionization detectors sounded sooner in open, flaming fires and that photoelectrics sounded sooner in smoldering fires. Many experts recommend changing smoke alarms every ten years.
The state of Oregon has some of the most comprehensive requirements in the nation regarding smoke alarms in residential properties being sold and in rental properties. Ionization smoke alarms are required to have a "hush" button and a 10 year battery if battery powered.