Photoelectric & Ionization Smoke Alarms

How They Work

• Ionization smoke detectors incorporate a small electrical current generated between two metal plates inside the devices. When smoke interrupts the current, an alarm triggers, warning residents of a potential fire hazard.

  Photoelectric smoke detectors generate a small beam of light and contain a light receptor inside. If rising smoke blocks the light from reaching the receptor, an alarm sounds.

Strengths and Limitations

• Fire Safety.gov reports that ionization smoke detectors respond more effectively to fast burning fires involving high flames. Photoelectric fires respond more effectively to smoldering fires burning over time. However, the National Fire Protection Association concludes that both types of smoke detectors provide adequate warning for evacuation in most structure fires.

  Both types of smoke detectors often perform ineffectively in kitchens, wood shops, shower rooms or any other ares in which residual cooking smoke, heavy steam or dust cause false alarms to sound. In these areas, heat detectors, which sound alarms based on sharp temperature changes, work best.

Where to Install

• Whether using ionization or photoelectric types, the National Fire Protection Association recommends installing smoke alarms on all levels of a home, particularly outside of all sleeping areas. Hanging the detectors at the highest point of rooms on walls or ceilings increases performance as smoke naturally rises. Smoke detectors mounted on ceilings work best when installed at least 4 inches away from every wall. In cases where wall mounts remain the only option, the NFPA recommends installing alarms about 12 inches away from the ceiling.

Best of Both Worlds

• Several smoke alarm manufacturers design the devices with both ionization and photoelectric technology inside, enhancing the ability of the detectors to respond quickly in all types of fires. Some even incorporate heat detector technology.

Why They're Important

• Regardless of the type of smoke detector used, the devices remain important life-saving tools. The NFPA reports that more than 40 percent of all home fire fatalities occurred in structures with no smoke alarms. The association also indicates that the death rate for every 100 fires was twice as high in homes lacking operating smoke detectors.