February 2008
Alarm types
Smoke alarms use two types of sensors—ionization and photoelectric. We recommend that you install smoke alarms with both types of sensors or install dual-detection units, which combine the
two. Smoke alarms have a limited life and should be replaced every 10 years. While a few models come with lithium batteries
designed to last the life of the alarm, most require annual battery replacement.
Ionization sensors ($20 and up) are better at detecting small particles that are typically present in fast, flaming fires, such as burning paper or fires started with an accelerant.
Photoelectric sensors ($20 and up) are more sensitive to large particles typically found in smoldering fires, such as those that start in a couch or bed.
Dual-detection alarms ($25 and up) combine ionization and photoelectric technologies. Only a limited selection of models exists at this time but they are available in battery and hardwired models.
Carbon monoxide alarms ($30 and up) use sensors to detect the level of carbon monoxide in the air and sound an alarm based on the level detected and the time spent at that level. Look for models with digital displays. Alarms should meet Underwriters Laboratories Standard 2034 certified by an independent lab such as UL, ETL or CSA; check the package. The standard became tougher in 2007.
One of the complaints about early-generation CO alarms was the number of false alarms those devices used to sound. The latest alarms won't sound unless the CO level exceeds 30 parts per million for 30 days. Today's alarms will also warn you within 4 hours at 70 ppm or within 15 minutes at 400 ppm. New standards in the works will require that CO alarms have an end-of-life signal that will tell you when you need to replace it. A rule of thumb is to replace your CO alarms every 5 years.
Combination smoke and CO alarms are alarms that combine smoke and CO detectors. They are available in these configurations: CO and ionization, and CO and photoelectric. If you buy a combination CO-ionization alarm, it is recommended that you also get a photoelectric unit, and vice versa. Their main attraction is likely the reduced number of alarms to place in the home. But many CO alarms mount in the typical wall outlet placed low on the wall while the optimum smoke alarm placement is on or near the ceiling.
Ionization sensors ($20 and up) are better at detecting small particles that are typically present in fast, flaming fires, such as burning paper or fires started with an accelerant.
Photoelectric sensors ($20 and up) are more sensitive to large particles typically found in smoldering fires, such as those that start in a couch or bed.
Dual-detection alarms ($25 and up) combine ionization and photoelectric technologies. Only a limited selection of models exists at this time but they are available in battery and hardwired models.
Carbon monoxide alarms ($30 and up) use sensors to detect the level of carbon monoxide in the air and sound an alarm based on the level detected and the time spent at that level. Look for models with digital displays. Alarms should meet Underwriters Laboratories Standard 2034 certified by an independent lab such as UL, ETL or CSA; check the package. The standard became tougher in 2007.
One of the complaints about early-generation CO alarms was the number of false alarms those devices used to sound. The latest alarms won't sound unless the CO level exceeds 30 parts per million for 30 days. Today's alarms will also warn you within 4 hours at 70 ppm or within 15 minutes at 400 ppm. New standards in the works will require that CO alarms have an end-of-life signal that will tell you when you need to replace it. A rule of thumb is to replace your CO alarms every 5 years.
Combination smoke and CO alarms are alarms that combine smoke and CO detectors. They are available in these configurations: CO and ionization, and CO and photoelectric. If you buy a combination CO-ionization alarm, it is recommended that you also get a photoelectric unit, and vice versa. Their main attraction is likely the reduced number of alarms to place in the home. But many CO alarms mount in the typical wall outlet placed low on the wall while the optimum smoke alarm placement is on or near the ceiling.
