A recent study showed that photelectric smoke alarms had an 8-fold lower rate of false alarms than ionization smoke alarms.
In addition to being an inconvenience, the false alarms also pose a threat because people are more likely to disconnect them, because of the nuisance of false-alarms. Ionization alarms were found to be nearly 5 times as likely to be disconnected than photoelectric alarms.
Western Journal of Medicine August, 2000;173:89-92
Every smoke alarm sold states right on the outside of the box which type it is. There are more of the ionization type around because they are cheaper. If you have one installed already and are unsure which type it is, all you have to do is look at the underside (side where batteries are or AC connection is) and see if there is a warning or notice about the radioactive material. ALL ionization devices are REQUIRED by US federal law to put a standard notice or warning . It will say something like "This product contains 0.02mg of americium ...."
Also, don't forget about carbon monoxide (CO) detectors as well. They are also very important to keep your home safe. Low level CO poisoning often goes undetected and may cause many adverse health effects.
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