There are two types of smoke alarm detection technologies fitted into New Zealand homes; ionization smoke detection and photoelectric smoke detection.
Ionization smoke alarms
Ionization smoke alarms are generally more responsive to flaming fires and most commonly fitted into NZ homes. Research has shown that ionization alarms are not good at detecting fire in its early stages.
How they work: 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. When smoke enters the chamber, it disrupts the flow of ions, thus reducing the flow of current and activating the alarm.
Photoelectric smoke alarms
Photoelectric smoke alarms are generally more responsive to fires that begin with a long period of smoldering (called “smoldering fires”).
How they work: Photoelectric-type alarms aim a light source into a sensing chamber at an angle away from the sensor. Smoke enters the chamber, reflecting light onto the light sensor; triggering the alarm.
Source: NFPA Ebook: Rescue Dogs, Firefighting Heroes, and Fire Science Facts