The two most common smoke detection technologies are photoelectric and ionization.
Photoelectric detectors use light to detect fires through a light-sensing chamber. When the alarm detects smoke, it deflects an LED light into a photosensor. When the light hits the photosensor, an alarm begins to sound. Photoelectric detectors are best for smoldering fires, and are considered to be more effective because of this.
Ionization detectors are typically more responsive to flaming and fast-burning fires. According to the National Fire Prevention Association, “Ionization-type smoke alarms have a small amount of radioactive material between two electrically charged plates, which ionizes the air and causes current to flow between the plates.” Once smoke enters, the ions are disrupted and the alarm sounds.
Although photoelectric detectors are considered more effective, it’s best to have both in your building. There are also dual sensor detection systems that combine these two detection technologies into one device.