Jim K wrote:
getting Pd off with motion detecing IP cams sending 100s of emails of
moving bushes and sunshine/shade changes.

One of the IP cams has 2 channels for I/O - so I'm pondering how to send a
signal to it to take a snap when something goes across the cam;s field of
view.

PIR would be perfect but a very narrow "beam" is required to make sure I
get the subject in the centre of the frame... and the IP cam is not going
to be happy with 240v up its I/O - so ???

low voltage PIR? what from where?

Somewhere which sells parts for intruder/burglar alarms would be the obvious
place to start looking.

Most likely the 240v unit actually consists of a relay, cheap PSU and a low
voltage unit anyway.