Photoelectric and ionization are the primary smoke detector types that alert your family to potential fire danger. Although both types sound an alarm, they differ in two ways: their method of detecting smoke and their suitability to different areas in the home.
Photoelectric vs. Ionization
Photoelectric smoke detectors use light beams to sense the presence of smoke. The detectors aim a beam of light into a compartment that contains a sensor, with the beam angled away from the sensor. As smoke enters the detector, it disrupts the light beam by reflecting it onto the sensor, which triggers the alarm.
Ionization smoke detectors ionize the air in a chamber. The detectors use radioactive material sandwiched between electrically charged plates to create a current between the plates. As smoke enters the detector, it interrupts the flow of ions, which sounds the alarm. According to the U.S. Environmental Protection Agency, the amount of radiation in an ionization smoke detector is negligible, staying virtually intact for the recommended 10-year life of a detector.
Covering Your Bases
Some fires start slowly by smoldering and producing a lot of smoke, and other fires quickly erupt in fiery blazes. Although both types of smoke detectors alert to the presence of smoke, their responsiveness is different. Photoelectric smoke detectors detect smoky fires more quickly than ionization models. But for detecting fiery blazes faster, ionization detectors are superior. The University of Missouri Extension recommends that you install both types of smoke detectors in homes for optimal protection.
It used to be that to get the best protection you had to install two types of detectors in each location. And few people did that, resulting in limited coverage. But now you can simply buy dual-sensor smoke alarms that use both ionization and photoelectric technologies, giving you the protection of both in one alarm unit.
Another type of dual-sensor alarm combines carbon monoxide detection along with smoke detection, creating a combo unit that looks just like a standard smoke detector. Sounds perfect, but there's a drawback: these feature only either ionization or photoelectric smoke detection; they don't have both. For the best fire protection, you still have to install two units at each location: one combo unit with CO and smoke detection and a second smoke alarm that uses the other detection technology.
Builders of new homes are required to install hard-wired (tied into the home's electrical system) smoke detectors that are interconnected so that if one unit detects smoke and sounds its alarm all other units in the house automatically sound their alarms. All hard-wired alarms include battery backup so the alarms work during a power outage.
Smoke detectors powered by batteries alone--not hard-wired--are allowed by most building departments when homeowners simply want to add an alarm and are not remodeling the home. However, standard battery-powered units do not offer the added protection of interconnectivity. It's best to hard-wire and interconnect alarms whenever possible.
If you want to expand a hard-wired system and maintain interconnectivity, one option is to add wireless alarms. This requires installing a sender alarm onto the hard-wired system. Any added alarms are receivers and they're connected to the sender via radio frequency. While the sender and receivers must be from the same manufacturer, they can be added to existing systems of other brands, in most cases.
Required locations for smoke detectors:
- At least one alarm on each floor of your home.
- One alarm in each bedroom and one in hallways adjoining bedrooms.
- Include a photoelectric smoke detector inside the bedrooms of smokers.
Additional locations, as desired or as required by local building code:
- Unfinished attics and other unconditioned spaces
Note: Due to the likelihood of nuisance alarms in garages and kitchens, heat-detection alarms, rather than smoke detectors, may be recommended.
- U.S. Environmental Protection Agency: Photoelectric Technology
- U.S. Environmental Protection Agency: Ionization Technology
- U.S. Environmental Protection Agency: Smoke Detectors & Radiation
- University of Missouri Extension: Residential Fire Detection
- Consumer Reports: CO & Smoke Alarm Buying Guide
- Kentucky Injury Prevention and Research Center: Smoke Alarms
- Photo Credit Lasse Kristensen/iStock/Getty Images
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