PIRs are very touchy things. I had a portable one to act as an alarm/ beacon
and it seemed to go off for no apparent reason at all. As I recall they work
by comparing the infra red received in a kind of striped group of sensors,
so presumably if, for example there is a draft and something hotter or
colder moves so its intermittently being seen by different parts, then it
sets the thing off.
Brian

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This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please!
"JohnW" wrote in message
...
I bought one of these Screwfix LEDs too. I took it back because the light
randomly came on at night and sometimes stayed on. Changed it for the one
without PIR and fitted separate PIR from Toolstation. No further problems,
and detection better as PIR is mounted lower down.

John