It’s a good idea to change smoke detector batteries when we adjust clocks for daylight savings time because it creates an easy, consistent reminder to perform a life-saving maintenance task.

There are two main types of smoke detectors, and each works differently:

Ionizing Smoke Detectors

Inside the detector, there’s a small amount of a radioactive material between two electrically charged plates. This material ionizes the air, creating a tiny electrical current that flows between the plates. When smoke enters, the particles attach to the ions, disrupting the current. The drop in current triggers the alarm.

Photoelectric Smoke Detectors

A light source (usually an LED) and a light sensor are positioned at an angle inside a chamber. In normal air, the light doesn’t hit the sensor directly. When smoke enters, the particles scatter the light so that some of it reaches the sensor. The sensor detects the light, which triggers the alarm.

Combination Detectors

Many modern smoke detectors use both technologies to detect both types of fires quickly and reliably.

Power Sources

Smoke detectors can be battery powered or hard wired: Battery powered detectors need regular battery changes while hard wired detectors are connected to the home’s electrical system, often with battery backup.