There are three different types of smoke detectors commonly found for sale: photoelectric, ionization, and combination. Ionization detectors utilize a small amount of radioactive material to create air flow between two electric plates. When smoke is drawn into the detector it changes the flow, sending the detector into alarm. Ionization detectors tend to work best for fires that flame up quickly. Photoelectric detectors utilize a beam of light within, when smoke enters the chamber; it reflects light into a sensor, sending the detector into alarm. Photoelectric detectors tend to work best on slow smoldering fires. Combination detectors utilize both ionization and photoelectric technology in one detector.
The National Fire Protection Agency (NFPA) suggests using both technologies in your home as you cannot predict which type of fire you may have. More information can be found on the NFPA website referenced below. NFPA smoke detector information