"Dead air" may prevent smoke from reaching the smoke detector. To avoid this, follow the instructions below to install your smoke detector.
On the ceiling
Install the smoke detector as close to the center of the ceiling as possible. If this isn't possible, install the smoke detector at least 300 mm away from a wall or corner.
On the wall (if permitted by building regulations)
The top of the smoke detector should be installed 102 to 300 mm lower than the ceiling boundary, below the typical "dead air" area.
On a pointed or sloping ceiling
Install the first smoke detector less than 0.9 meters from the highest point of the ceiling, measuring horizontally. Depending on the length, angle, etc. of the slope of the ceiling, several smoke detectors may be required.