nedis DTCTSL40WT Mode D'emploi page 6

Sloping ceiling mounting
Dead air at the peak of sloped ceiling may prevent the smoke from reaching the alarm in time to provide an early warning. So
install smoke alarms on the ceiling where 1 m(3 feet) from the highest point of a ceiling.
Dead air area
DTCTSL40WT_PhotoelectricSmokeAlarm_Manual
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