Well I suppose one the more interesting facets of an integrated system is the ability to fuse together various sources of information, so more sources can perhaps improve accuracy, though how this information is managed is of course the tricky bit ...
Anyhow, regarding the speed of reaction of PIR only based detection - it depends how you place the PIRs. If a PIR is mounted close to a doorway and facing away from the door (or perhaps even above the door), then when the door is opened it can cause the PIR to trigger due to the sudden fluctuation of air temperatures in the vicinity of the sensor or perhaps even moving IR reflections/occlusions by the door body. Even if this doesn't happen, then with a PIR close to the door the person will trigger the PIR pretty soon after their body crosses the threshold. So reaction can be improved by PIR positioning. Of course one can also have multiple PIRs in a room.
Anyhow, regarding the speed of reaction of PIR only based detection - it depends how you place the PIRs. If a PIR is mounted close to a doorway and facing away from the door (or perhaps even above the door), then when the door is opened it can cause the PIR to trigger due to the sudden fluctuation of air temperatures in the vicinity of the sensor or perhaps even moving IR reflections/occlusions by the door body. Even if this doesn't happen, then with a PIR close to the door the person will trigger the PIR pretty soon after their body crosses the threshold. So reaction can be improved by PIR positioning. Of course one can also have multiple PIRs in a room.
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