PIR setting off alarm but can't find out why

jem16

I had a new alarm installed in April of this year. It has 4 PIRs on 3 separate zones plus door contacts on the outer doors. It is not connected to the telephone line at all.

At the beginning of July the alarm went off around midnight. It was one of the zones which has one PIR in each of the main living rooms. Nothing was apparent as to the cause. Around 5/6 weeks later the exact same zone caused an alarm again so I called out an engineer. He checked the wiring which all seemed fine except for one of the PIRs where the wire was inserted into the contact but had not been screwed shut - this was fixed.

Unfortunately the exact same thing happened one week later. This time the engineer replaced the circuit boards in both PIRs in that zone. Last night exactly the same thing happened although this time the contraol panel showed 2 zone leds lit. The first one was the same zone as the last 3 occasions but this time one other zone with a PIR was lit. Again no apparent cause.

On each of the last 3 occasions the alarm has gone off on a Wednesday night always around 11:30pm - 12:30am. I can't remember if the first time was also a Wednesday or not.

It has never gone off during the day and each time it has happened I can't find a cause. There is nothing in either room that could move and absolutely nothing amiss.

Has anyone any idea what might be causing this? It's certainly strange that the last 3 occasions have been on the same night of the week around the same time. I can think of nothing though that would cause it.

gas4you

Have you got any pets? If so are the PIR's pet rated?

jem16

No pets at all.

muckybutt

as daft as it sounds spiders can set them off, but if its occurring at around the same time then it could be a mains spike or some other kind of electrical interference.

It might be worth investing in double knock detectors or a combined microwave / PIR detector.

Double knock require the detector to be triggered twice before it goes into alarm, similar sort of thing with a combo detector,it requires both the microwave and the infra red detection to be activated before it will alarm.

jem16

muckybutt wrote: »

as daft as it sounds spiders can set them off, but if its occurring at around the same time then it could be a mains spike or some other kind of electrical interference.

I wondered if that was possible given the timing. It's just strange that from April to June there was no problem.

Perhaps I have a mouse who likes to visit on Wednesdays.

Although I'm now even more confused as last night two different zones apparently triggered the alarm at the same time. Wouldn't have thought that was p;ossible but it happened.

It might be worth investing in double knock detectors or a combined microwave / PIR detector.

Double knock require the detector to be triggered twice before it goes into alarm, similar sort of thing with a combo detector,it requires both the microwave and the infra red detection to be activated before it will alarm.

I shall look into this - thanks.