There are two types of smoke alarms: ionization and photoelectric.
Both ionization and photoelectric alarms are effective smoke sensors. Both types of smoke alarms must pass the same tests to be certified.
Ionization alarms respond more quickly to flaming fires with smaller combustion particles; photoelectric alarms respond more quickly to smoldering fires. In either type of alarm, steam or high humidity can lead to condensation on the circuit board and sensor, causing the alarm to sound.
Ionization alarms are less expensive than photoelectric alarms, but some users purposely disable them because they are more likely to sound an alarm from normal cooking due to their sensitivity to minute smoke particles.