What's the difference between photoelectric and ionization smoke detectors?

Photoelectric sensors respond faster to smoldering, smoky fires (common with furniture and electrical sources), while ionization sensors react faster to fast-flaming fires. Many fire-safety bodies recommend combination coverage. Several picks here use photoelectric sensing, and some combine smoke detection with carbon monoxide sensing, but none of the candidates in this pool documented dual ionization-plus-photoelectric smoke sensing in the supplied data.