Optical type: when the smoke cuts the optical detection path, and unbalance in the detector current loop raises a smoke alarm. These type detectors are sensitive to larger particles of combustion 0.5 to 10 microns. It is suitable for applications where thermal turbulence can be expected.
Radio active type: when the smoke is detected by the radio active substance, the unbalance in the detector current loop raises a smoke alarm. This type of detectors are sensitive to air movement greater than 5m/sec. It is normally installed with the photoelectric (optical type) type smoke detectors.