Research

Residential smoke alarms must be photoelectric.

Ionisation alarms' won't reliably detect fire in the early, smouldering stage.

Photoelectric alarms are even more important in recreational vehicles due to the ionisation alarms' unacceptably high rate of ". . .nuisance alarms from cooking which cause disablement."
Chief Joseph (Jay) Fleming (Retired)  Boston Fire Department, MA, U.S.A.