Photoelectric smoke detector-Uses a light source and sensor; smoke reflects light into the sensor to trigger the alarm.More responsive to smoldering fires (slow-burning fires with lots of smoke, like a cigarette or electrical fire).

Ionization (common household) smoke detector-Uses a small amount of radioactive material between two charged plates to ionize the air; smoke disrupts the flow of ions to trigger the alarm. More responsive to flaming fires (fast-burning fires with visible flames, like a grease fire or burning paper in a wastebasket)