pir false alarms

["joble_5@xxxxxxxxxxx" <joble_5@xxxxxxxxxxx>]

Hi,

we have an alarm for 2,5 years now. It is a Rokonet system. The PIR
detector's used are Pyronix Magnum Ultra.

It worked fine for more than 2 years, but last summer we had false
alarms almost once per week. Always on the same sensor. Sensor was
replaced by the installer, but next night there was again a false
alarm.

The Pir is now replaced by a dual detector, and this detector seems to
work well.

The next week we had false alarms with both the two other PIR's. So
they are also replaces by dual's.

Now it has worked fine for 3 months. But the installer sends us a bill
for the replacement of the first detector. And i think another bill for
the two others will follow. Together this is the 25% of the price of
the system! I do not think this is normal after 2,5 years. (The
warranty of the system is 1 year, but on the pyronix site i read the
pir detectors come with 5 years of warranty)


I want to argue with the installer but first i want to learn more about
the problem. So i have some questions:

Is it possible that a fly triggers the pir?
Can this problem be due to bad adjustment of the pir or the use of the
wrong lenses?
Can the reason be in the rokonet system instead of in the PIR's?
Any other ideas???


Thanks in advance...
Joble