- $99 for a dryer-vent cleaning and smoke-detector inspection ($199 value)
Smoke Detectors: Fire Safety’s Two Technologies
Although smoke detectors may have different looks or sounds, most are triggered by one of two kinds of sensors. Read on for a breakdown of both types that may be found in your home.
Ionization Detectors: A Half-Life That Saves Lives
The more common of the two, ionization smoke detectors harness a force that may seem counterintuitive to home safety: nuclear radiation. Inside the detector, a tiny particle of a radioactive isotope—typically americium-241—constantly generates radiation known as alpha particles. These particles interact with the oxygen and nitrogen atoms in the air to create ions with negative and positive charges, resulting in a small electric current. If any smoke particles reach the chamber, they immediately neutralize the ions and nullify the current, triggering the alarm. This style of alarm is more effective in detecting smaller smoke particles, which typically emanate from hot, fast-moving blazes fueled by highly combustible materials.
Photoelectric Detectors: Smoke as Mirrors
As the name suggests, photoelectric detectors rely on smoke’s interaction with light to trip the sensor. However, while it’s logical to think the detector senses when smoke blocks out a beam of light, it actually works because of smoke’s ability to deflect light. In this model, the sensor mechanism is typically a T-shaped chamber in which a constant beam of light traces across the top horizontal bar. A light sensor occupies the vertical leg, untouched by the perpetual beam above. When smoke drifts into the chamber and reaches the horizontal bar, it scatters the light, directing some beams into the light sensor and triggering the horn. This style is particularly adept at detecting the thicker smoke of slow-burning, smoldering flames such as those caused by a particularly heated sibling rivalry.