Looking for cause of false alarm

manofthefora

Five nights ago (9pm), when I was away, the house alarm went off.
The log indicated a specific room which is monitored by a KX15DT Pyronix device (has PIR and Microwave detection).
The log indicated an alarm event at approx 9.02, 9.04, 9.06 and 9.08pm.
There was no evidence of any disturbance.
It has worked without fault for about eight years.
Now, on the evening in question there was a mobile phone on a table in the room, screen facing up without a cover. It was very low on charge. No one being there, it would finally have died.
So I am wondering if the Pyronix detection device is faulty OR if it could be triggered by a mobile phone dying. I think these phones just die quietly so unlikely cause.

I am pretty certain there were no other disturbances on the night. I have external CCTV cameras and there was no bad weather or other recorded events. Heavy curtains were drawn and room in total darkness (9pm).
Any thoughts please?
Are these devices prone to ageing and producing random false alarms?
It has been in use since then without any problems.
MOTF

KoolKid

Generally when a PiR goes faulty if will stay faulty.
Has it activated since?
I have never seen a mobile phone activate a PiR like that.

manofthefora

AH! Thank you Koolkid. That's what I want to hear.
It has worked perfectly since the false alarm five days ago.
So, something triggered it four times.
I have since made phone calls to the mobile while it is in the room and it has not triggered the alarm.
Just had a thought: would a spider trip the alarm? Spinning a web near it?
I see them all the time on the CCTV.
MOTF

P.S.
Further research points almost certainly to spiders (or A spider!)

KoolKid

Spiders around a PiR (or inside it) would be a common culprit.