New Smoke Alarms Are Better at Detecting Fires but Still Beep for Bacon

September 18, 2024

A new standard for smoke alarms, which went into effect on July 30, requires smoke detectors to be more sensitive to all types of fire and to have fewer nuisance alarms from cooking.

NIST research in a kitchen fire laboratory shows that these smoke alarms still produce nuisance alarms during cooking.

NIST experts offer a few tips to minimize nuisance alarms in your home.

NIST researcher Emma Veley heats up a pan of bacon in the lab to see how long it takes to set off each of the 12 smoke alarms behind her on the ceiling.
Credit: R. Eskalis/NIST

Armored with safety glasses, hearing protection, and a fire-retardant lab coat, fire researcher Emma Veley carefully cradled a frying pan of raw bacon into a laboratory surrounded by wires and sensors. Mounted on the ceiling above, 12 smoke detectors waited patiently in a neat row. Veley closed the door behind her, placed the pan on a hot plate, and turned up the heat. Watching her through a large window in the next room, Amy Mensch started a timer and monitored the computer readouts that would show exactly when each alarm would "smell the bacon.”

“Modern smoke alarms are really good at detecting fires. However, they have a challenge with not detecting cooking, because cooking is almost a fire,” said Mensch, who is the lead author on a new technical report from the National Institute of Standards and Technology (NIST) about how well the latest generation of smoke detectors avoids nuisance alarms. Odds are you’ve experienced one of these nuisance alarms yourself when cooking or shower steam sets off a smoke alarm. But they’re more than just annoying; they can be a real concern for fire safety.

“Studies have found that people who repeatedly have these nuisance alarms tend to disable their devices,” explained Mensch, “and when an alarm is disabled, it can’t do its main job of alerting people of a real fire.”

Raising the Standards for Smoke Alarms

If you examine the back of a smoke alarm, you should see a label saying that it meets UL 217, the manufacturing standard for smoke alarms. This standard is a list of rules to make sure that any smoke alarm performs to a minimum acceptable level. It’s maintained by an organization called UL Standards and Engagement with input from a technical panel made up of a wide variety of fire safety experts and from manufacturers and researchers, including some at NIST.

NIST has had a large role in developing and advocating for smoke alarms since the 1970s when the agency funded comprehensive field tests for smoke alarms. Those tests laid the foundation for the first version of the UL 217 standard. Since then, the wide adoption of home smoke alarms is one of the greatest success stories in the history of fire safety. Between 1975 and 2000, the percentage of homes with smoke alarms rose from less than 10% to over 95%. In that same period, the number of deaths from home fires was cut in half. On June 30, 2024, a new standard for smoke alarms, the eighth edition of UL 217, went into effect. For the first time, this standard contains a test for reducing nuisance alarms.

Have you ever had a smoke alarm go off while you're cooking? Nuisance alarms are more than just annoying; they're dangerous! People who have a nuisance alarm problem may deactivate the alarm, putting themselves in danger of a real fire.

“There were a few reasons the standards technical panel thought the smoke alarm standard should be updated,” explained NIST’s Thomas Cleary, who has regularly participated in panel discussions. “The first reason was that new materials in the home are causing different kinds of house fires.” For example, modern sofa cushions are often stuffed with polyurethane foam, which burns more quickly than the cotton or horsehair-stuffed cushions used in the first smoke alarm tests.

The panel also wanted to make sure that different types of smoke alarms are equally effective. The two main types of smoke alarms, photoelectric and ionization, have traditionally had different strengths, with the former better at detecting smoldering fires and the latter better at sensing flaming fires. Consumers had to decide between the two, and NIST even recommended installing both types of alarms simultaneously or a dual sensor alarm for added protection.

To eliminate this confusion, the panel designed the new standard to ensure that all detectors are good at detecting smoke from both kinds of fires. But they worried that this requirement would make alarms too sensitive, so as a counterbalance they also introduced a new nuisance alarm test to the standard. Tests like these are paid for by manufacturers and performed in nationally recognized testing laboratories. To pass this test, two standardized hamburger patties are broiled 10 feet away from a smoke alarm. The alarm passes the test if it doesn’t go off.

NIST Tests the New Generation

There are now several smoke alarms on the market that meet this latest edition of the standard. NIST ran a series of experiments to see how they compare to the previous generation.

Older smoke alarms generally are not sensitive enough to meet the new standard. In 2016, NIST tested 45 alarms from the previous generation, and not one of them could pass the new standard.

This implies that alarms that do pass the new standard should be better at detecting smoldering and flaming fires. But the hamburger test for nuisance alarms is new, and the NIST team wanted to directly compare the new alarms with the old ones to see how well this new requirement helped reduce false alarms during cooking.

“Modern smoke alarms are really good at detecting fires. However, they have a challenge with not detecting cooking, because cooking is almost a fire.” —Amy Mensch, mechanical engineer at NIST

In the NIST kitchen fire lab, researchers cooked a variety of foods they thought might activate the smoke alarms, from bacon to toast to grilled cheese. When it comes to nuisance alarms, the new devices perform about the same as the old ones.

“It was a mixed bag,” said Thomas Cleary. “Compared to the old alarms, the new alarms weren't universally better at not going off during cooking.”

Overall, this means the standard is working. The new alarms are designed to be more responsive toward more kinds of fire without also increasing the rate of nuisance alarms.

NIST Tips for Reducing Nuisance Alarms

If you have problems with an annoying smoke detector at home, Cleary says there are a few things you can do to reduce them. The first is location. If possible, place your smoke detectors at least 6 feet, and ideally 20 feet, away from the cooking area. Making sure your home is well ventilated will also help reduce nuisance alarms. If all else fails, many modern smoke alarms come with a “hush button” you can press to temporarily deactivate them.

The researchers also discovered another surprising tip: upgrading your stove. During the study, the researchers had a hard time getting the stovetop, which is a newer model, to bring the food to a high enough temperature to set off the smoke alarms. For some experiments they even had to switch to a hot plate to generate the smoke they needed. As the fire safety standards for appliances around the kitchen continue to improve, they may also reduce nuisance alarms as an added benefit.

Adoption of the new smoke alarms will be gradual. Manufacturers are still allowed to sell their stock of old smoke detectors. The new standard applies only to newly manufactured detectors. And there’s no law that says you need to immediately upgrade.

“People do not immediately change their smoke alarms,” said Cleary. “It'll take many years for everyone to have the newer style alarms in their homes.”

In the meantime, even fire alarm researchers sometimes have to deal with unwanted alarms. “Earlier this year, I invited a whole bunch of people over for pizza night,” said Veley, “and my smoke alarm went off with everybody hanging out in my apartment.”

Report: Amy E. Mensch, Emma M. Veley and Thomas G. Cleary. Performance of New Smoke Alarms and Aerosol Measurements for a Range of Nuisance Cooking Sources in a Mock Kitchen. NIST Technical Note 2305. Sept. 2024.