Dave Plowman wrote:

Some give you a choice of lenses - the idea being to avoid ground level
and therefore pets. Of course, cats can jump up on things. But if yours
are this type you might be able to buy the lenses only and experiment.
A pal who had several cats avoided PIRs altogether and relied on shock
sensors. But had loads of false alarms.

The ones we have fitted apear to work on the infra red 'mass' rather than
poisition. I've lost the leaflet that came with them (naturally) but they
have an upper weight limit of something like 30kg and anything above this
will trigger the alarm. They appear to be fairly reliable so far as we
haven't had any false alarms from the cats jumping onto window sills or
worktops so they don't appear to be overly sensitive to position.
--
Regards

Tony Hogarty
(take out garbage to reply)