There are two types of smoke alarm sensor technology.
Ionization sensing alarms may detect fire particles (associated with fast flaming fires) sooner than photoelectric alarms. Photoelectric sensing alarms may detect visible fire particles (associated with slow smoldering fires) sooner than ionization alarms. Studies show both types will effectively detect either type of fire. Kidde offers photoelectric and ionization smoke alarms, as well as a dual-sensor model, which incorporates both technologies.
The NFPA indicates that altitudes greater than 3,000 feet may have an impact on ionization alarms. Accordingly, it is recommended that a photoelectric alarm be used in high altitudes.