The ionic smoke alarm is more sensitive to the tiny smoke particles and can respond evenly to all kinds of smoke, while the photoelectric smoke alarm is more sensitive to the larger smoke particles and has a poor response to the smoke and black smoke.
When there is a big fire, there are more tiny particles in the air, and when it is smoldering, there are more larger particles in the air. If a fire occurs, a large number of small particles of smoke are produced, the ionic smoke alarm will alarm before the photoelectric smoke alarm. The time interval between the two smoke alarms is small, but the spread of such fires is extremely fast, and ionic smoke alarms are recommended in such places.
After another kind of smoldering fire, a large number of slightly larger smoke particles are produced, and the photoelectric smoke alarm will alarm first than the ion smoke alarm. It is recommended to install the photoelectric smoke alarm in such places.
If you want to combine the advantages of both, you can install both smoke alarms where smoke alarms are required.