Smoke, CO and Heat Alarms: What USFA and CPSC Say
When most people think of fire, the U.S. Fire Administration observes, they think of something bright, not the thick, black smoke that can quickly fill a home. The agency holds that fire deaths can be reduced by teaching people the basic facts about fire.
Smoke alarms sense the presence of smoke. CO alarms are designed to alarm before potentially life-threatening levels of carbon monoxide are reached. Heat alarms respond to high temperatures. And according to the U.S. Fire Administration, residents could have less than 2 minutes to escape a home fire once the smoke alarm sounds.
How Little Time a Home Fire Allows
The USFA states the escape window plainly. Residents could have less than 2 minutes to escape a home fire once the smoke alarm sounds. There is little time to escape, the agency says.
The USFA is also specific about what does the killing in a home fire. Smoke and toxic gases kill more people than flames do.
People ages 65 and over have an increased risk of dying in a fire, the USFA says. In 2020, older adults (65+) in the United States had a 2.5 times greater risk of dying in a fire than the total population. Having physical or mental impairments, using chemical substances such as medicines and alcohol, and living with smokers or in substandard housing are some of the risk factors the agency lists behind older adults’ greater vulnerability to fire injury and death.
Those numbers describe risk across a population, not any one household.
Two Ways a Smoke Alarm Senses Smoke
There are two types of smoke alarms in general use for home smoke alarms, the USFA says: photoelectric and ionization. They sense the presence of smoke differently. Flaming fires produce a different type of smoke than smoldering fires, the agency adds.
Both smoke alarms will detect the smoke from either a smoldering fire or a flaming fire, according to the USFA. What differs is speed. Ionization smoke alarms tend to respond faster to the smoke produced by flaming fires than photoelectric smoke alarms.
Photoelectric smoke alarms tend to respond faster to the smoke produced by smoldering fires than ionization smoke alarms. In some full-scale fire tests, the difference in the time to alarm between ionization and photoelectric smoke alarms was found to be trivial. In other full-scale fire tests, the difference in response time was considerable.
| Smoke alarm type | How the USFA describes it |
|---|---|
| Ionization | Tend to respond faster to the smoke produced by flaming fires than photoelectric smoke alarms |
| Photoelectric | Tend to respond faster to the smoke produced by smoldering fires than ionization smoke alarms |
| Dual sensor | Contains both ionization and photoelectric smoke sensors |
Source: U.S. Fire Administration
The USFA position statement does not rank the two. “We cannot state that one type of alarm is better than another because every fire is different,” it says.
Because no one can predict what type of fire might start in a home, the USFA recommends that every home and place where people sleep be equipped with either both ionization and photoelectric smoke alarms, or dual sensor smoke alarms, which contain both ionization and photoelectric smoke sensors. The agency also says the location of a smoke alarm within a home may be more important than the type of smoke alarm present, depending on the location of a fire.
Smoke, Carbon Monoxide, and Heat Alarms Compared
The agencies describe the three alarms differently, and they place them differently.
| Alarm | How the agency describes it | Placement or setting the agency describes |
|---|---|---|
| Smoke alarm | Senses the presence of smoke | Inside and outside each bedroom and sleeping area, on every level of the home, on the ceiling or high on the wall |
| Carbon monoxide alarm | Designed to alarm before potentially life-threatening levels of CO are reached | On every level of the home and outside sleeping areas; CPSC does not recommend kitchens or above fuel-burning appliances |
| Heat alarm | Responds to high temperatures | Described as ideal for garages |
Sources: U.S. Fire Administration; U.S. Consumer Product Safety Commission
In a garage, the two fire devices part ways. Smoke alarms are not required, or designed for use, in garages, the USFA says. Smoke alarms in garages can sound because of a change in temperature and humidity, as well as dust, fumes and insects.
Heat alarms are made to not be affected by these conditions, according to the USFA. Heat alarms (detectors) respond to high temperatures and are ideal for garages, the USFA says. Many heat alarm models can be connected to a home’s fire detection system so that if the heat alarm sounds, the smoke alarms will as well.
Both agencies describe interconnected alarms. With interconnected smoke alarms, the USFA says, when one sounds, they all sound. CPSC says the same of interconnected CO alarms.
There are also alarms for people with hearing loss. These alarms may have strobe lights that flash and/or vibrate to alert those who are unable to hear standard smoke alarms when they sound.
How Smoke Alarms Are Powered and Replaced
Smoke alarms are powered by battery or by the home’s electrical system, the USFA says. A battery-powered alarm runs on either a disposable 9-volt battery or a nonreplaceable 10-year lithium-ion (“long-life”) battery. Hardwired alarms usually have a backup battery.
Age matters too. Smoke alarms need to be replaced 10 years from the manufacture date, according to the USFA.
The USFA gives some general maintenance tips for all three setups. For a smoke alarm powered by a 9-volt battery, the tips are to test the alarm monthly, replace the batteries at least once every year, and replace the entire smoke alarm every 10 years. For one powered by a 10-year lithium-ion battery, they are to test the alarm monthly and replace the entire smoke alarm according to the manufacturer’s instructions.
For a smoke alarm that is hardwired into the home’s electrical system, the tips are to test the alarm monthly, replace the backup battery at least once every year, and replace the entire smoke alarm every 10 years. A smoke alarm only works when it is properly installed and regularly tested, the agency says.
The agency also describes what a missing battery means. A smoke alarm with a dead or missing battery is the same as having no smoke alarm at all. Disabling a smoke alarm or removing the battery can be a deadly mistake, in the agency’s words.
Some fire departments offer reduced-price, or even free, smoke alarms, the USFA notes. And a city, county or state may require a specific type of alarm.
Carbon Monoxide and Carbon Monoxide Alarms
Carbon monoxide (CO) is a deadly, colorless, odorless, poisonous gas, CPSC says, produced by the incomplete burning of various fuels, including coal, wood, charcoal, oil, kerosene, propane, and natural gas. On average, more than 200 people in the United States die every year from CO produced by non-automotive consumer products.
The initial symptoms of low to moderate CO poisoning are similar to the flu, but without the fever, according to CPSC. The symptoms the agency names include headache, fatigue, shortness of breath, nausea, and dizziness. Symptom severity is related to both the CO level and the duration of exposure, CPSC says.
CO alarms always have been and still are designed to alarm before potentially life-threatening levels of CO are reached, according to CPSC. A CO alarm can provide some added protection, but it is no substitute for proper use and upkeep of appliances that can produce CO. An alarming CO alarm is warning of a potentially deadly hazard, the agency says.
CPSC recommends battery-operated CO alarms or CO alarms with battery backup on every level of the home and outside sleeping areas. CPSC does not recommend installing CO alarms in kitchens or above fuel-burning appliances.
For CO alarms, using a test button tests whether the circuitry is operating correctly, not the accuracy of the sensor, CPSC says.
CO alarms have a recommended replacement age, which can be obtained from the product literature or from the manufacturer. Newer alarms have an end-of-life signal that will indicate when the alarm needs to be replaced.
For symptoms, a doctor is the right place to take the question; for a specific appliance, a qualified service person is.
Smoke, carbon monoxide, heat: three alarms, described by two agencies. For a home fire, the USFA’s figure is less than 2 minutes to escape once the smoke alarm sounds.
This article is general information, not professional advice. For decisions about your money or health, consult a qualified professional.