"Bill Woods" wrote in message
...
I have a PIR for sensing people in our garden. I want to have the
PIR located behind glass or plastic.

If the PIR is behind glass then the glass blocks the heat which
triggers it. I image a clear plastic sheet would also block heat.

Is there some special plastic (like that used in the PIR's lens)
which can transmit heat?

I have a mini-IR camera and IR LEDs in a bluetit nestbox and use the bottom
of a plastic milk carton (the 4 pint/2 litre sort) to protect the LEDs. It
works fine - no obvious loss of IR. Of course PIRs might work on a different
part of the IR spectrum.

--
LSR