Conrad Electronic RM 100-2 BiDi-S Bedienungsanleitung Seite 54

Selecting an unfavorable mounting place causes the smoke
detector not to react and to set off the alarm only by a very high
smoke concentration.
This diminishes significantly the time available for rescuing
oneself and others or for extinguishing the fire.
Window sills, curtains or furniture have a strong impact on the
circulation of air, hence on the movement of smoke. They create
a zone of dormant air. For that reason, ascending smoke does not
reach the smoke detector or it reaches it too late!
in principle, the installation of the smoke detector on the ceiling
in the middle of the room is recommended. The mounting position
must not be directly under lights (e.g. halogen lamps).
In ordre to check the acoustic quality of the selected place of installation, the
alarm can be set off (see installation) while somebody is sleeping in a bedroom.
The smoke detector must awaken the sleeping person! It
must not be only audible!
Furthermore, the radio reception at the place of installation of each smoke
detector must be checked (e.g. reception among smoke detectors of identical
construction "RM 100-2 BiDi-S" or reception from the radio system "FAZ 3000",
"HMS 100" or FHZ 1000".

In general, most single family houses do not encounter reception
problems. As described in chapter 15 "(indications relevant to
radio range"), radio reception can encounter many restrictions
For example, ceilings with reinforced concrete or electric floor-
heating systems can hinder the reception of several floors.
Also electric lines, devices or metal objects have a negative
impact over the range.
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