Best Smoke Detector: Ionization, Photoelectric Or Dual Sensor?

Types of Smoke Detectors

The two primary types of residential smoke detectors contain either ionization or photoelectric sensors. Each type of smoke alarm detects distinctly different types of fires, so dual sensor alarms, which utilize both types of sensors, have risen in popularity.

Smoke detectors consist of two basic parts: a sensor to sense smoke and a loud electronic alarm. They can run off of a 9-volt battery or be hardwired into a 240-volt house current. The batteries, or backup batteries in a hardwired system, should be tested on a regular basis and replaced at least once each year.

Additionally, some smoke alarms are designed to meet the needs of people with hearing disabilities. These alarms use strobe lights and vibrations to alert anyone unable to hear standard smoke detectors.

Type 1: Ionization Smoke Detector

Ionization smoke detectors contain a very small amount of americium-241 within an ionization chamber. They create an electric current between two metal plates, which sound an alarm when disrupted by smoke entering the chamber. Ionization smoke alarms can quickly detect the small amounts of smoke produced by fast flaming fires, such as cooking fires or fires fueled by paper or flammable liquids.

This type of smoke detector, which is commonly used in kitchens, is prone to nuisance tripping. For example, we’ve all experienced the loud annoying chirping when we leave a cake in the oven too long or add oil to an extremely hot pan. When this happens, people are more prone to disable the alarms.

Type 2: Photoelectric Smoke Detector

Photoelectric smoke detectors contain a light source in a light-sensitive electric sensor, which are positioned at 90-degree angles to one another. Normally, light from the light source shoots straight across and misses the sensor. When smoke enters the chamber, it scatters the light, which then hits the sensor and triggers the alarm.

Photoelectric smoke detectors typically respond faster to a fire in its early, smoldering stage – before the source of the fire bursts into flames. These detectors are more sensitive to the large combustion particles that emanate during slow, smoldering fires, which usually occur at night when people are asleep.

Type 3: Dual Sensor Smoke Detector

Dual sensor smoke detectors include both ionization and photoelectric sensors, so they should adequately alert homeowners of a smoldering fire or a fire with active flames. Some safety organizations have previously recommended these smoke alarms, because they should cover a broad range of fires.

However, there are no industry standards for setting the individual sensor sensitivity in dual sensor alarms. This means that a dual sensor alarm could have a non-functional ionization sensor, but as long as the photoelectric sensor works, it still meets the national standards developed by Underwriters Laboratories (UL).


Best Smoke Detector: Which One Should You Buy?

The technology used in ionization smoke detectors leads to a delayed warning in smoldering fires, which can lead to greater loss of life. Ionization detectors are also weaker in high airflow environments, so the delay may be even longer. Photoelectric smoke alarms are more effective at warning of smoke from smoldering fires and are less susceptible to nuisance alarms.

To be safe, most safety organizations recommend homeowners replace all ionization, dual sensor, and unknown alarms with photoelectric smoke alarms.