Safety’s No Accident: A New Year’s Resolution Has Us Buzzing about Alarms and Detectors – Part 2: Dual-Sensor Alarms

by Jonathan Wilson

This is the second installment in a three-part blog series. Read part one here.

As I reported in an earlier blog, I planned to install sealed 10-year smoke alarms in our home to be in compliance with Maryland state law. I knew that I had replaced a battery-powered smoke in my home within the past 10 years. Further, also I knew that because it did not have a sealed 10-year battery, the alarm would now have to be upgraded. But as I assessed the situation, I learned two things: First, each floor of our home has been hardwired to the electrical panel for smoke alarms. The battery-powered smoke alarm I had replaced appears to have been installed by the former owner when for some reason, they did not replace the hardwired alarm on the second floor of our home. Second, because our home was built after 1975, I would need to replace the hardwired alarm to be in full compliance with Maryland state law. But what alarm should I install?

Different Types of Smoke Detectors

Smoke alarms can come with two different types of smoke detectors.

• Ionization detectors create a flow of ions within the device. When the ions are disrupted by smoke, the alarm sounds. Research has found that ionization sensors are best at responding to fast-burning, “flaming” fires.
• Photoelectric detectors have a light source within the device. When the light is reflected by smoke particles entering the chamber, the light sensor triggers the alarm. Research has found that photoelectric sensors are best at responding to slow-burning, “smoldering” fires.

As recently as 2012, about 90% of U.S. homes had a smoke alarm with an ionization sensor, about 5% had a photoelectric sensor, and the remainder of homes had no smoke alarm at all. Having no alarm certainly poses the highest risk, but people are now realizing that having the “wrong” type of sensor in the home can also have tragic results. Today, many groups including the National Fire Protection Association (NFPA), insurers, and the publishers of Consumer Reports recommend installing both types of alarms in our homes. Manufacturers are now selling devices that have both sensors, so the most efficient way to put both sensors in a home is to install these “dual-sensor” models.

Are We Safer with Dual-Sensor Alarms?

Some observers have questioned whether the dual-sensor models will alarm as quickly as models with the individual sensors. However, a 2009 study by the National Institute of Standards and Technology (NIST) and reviewed by NFPA found that “the assumption that sensors in dual alarms are always less sensitive than those found in individual photoelectric or ionization alarms is false. Typically, dual alarms respond before ionization alarms in smoldering fires and before photoelectric alarms in flaming fires.”

Knowing that a dual sensor would effectively protect my family’s safety, I started thinking more about the idea of having just one alarm per story in our home.¹ I had seen smoke alarms sold in combination with carbon monoxide (CO) detectors. Could a single alarm on the second floor address the risks of both fires and carbon monoxide poisoning? Unfortunately, the marketplace is not there just yet. Consumer Reports says it well: “Our challenge to manufacturers: Produce a single device that senses both kinds of fire and CO. Until then, combining various types of alarms offers the best protection.”

Next Steps in the Resolution for Home Safety

With this information in hand, I went ahead with purchasing and installing a dual-sensor hardwired smoke alarm. I also decided to seize the moment and practice what my organization preaches: Every home should have a CO detector installed. In my next blog, I’ll discuss my search for the optimal CO detector for our home.

Read Safety’s No Accident – Part 3.