Photoelectric X Ionization - Differences between Smoke Detector types

There are two smoke detector types: ionization and photoelectric. The main difference between the two is the type of fires they detect.

When the fire is still in the smoldering stage (before it breaks into flame), photoelectric smoke detectors respond faster.

In the case of fast flaming fires Ionization smoke detectors respond slightly faster.

This happens because they use different technology to detect and activate the alarm.

A photoelectric smoke detector aims a light source into a sensing chamber at an angle away from the sensor. Smoke enters the chamber, reflecting light onto the light sensor, and triggering the alarm.

An ionization smoke detector uses a radioisotope to ionize the air. If any smoke particles enter the open chamber, some of the ions will attach to the particles and not be available to carry the current in that chamber. An electronic circuit detects that a current difference has developed between the open and sealed chambers and sounds the alarm.

For each type of smoke alarm, the advantage it provides may be critical to life safety in some fire situations. Combination alarms provide ionization and photoelectric detection and the NFPA recommends installing combination alarms, or both types of alarms, in the home.