"Andrew Gabriel" wrote in message
...

8

Both conservatory and garage can be liable to false triggering from
PIR sensors, due to significant sources of heat causing movement of
hot air - conservatory from the sun, and garage from a parked car
with hot exhaust/engine. In these cases, a dual tech sensor (PIR
and microwave) may be necessary, although in a conservatory, careful
adjustment of microwave power will be needed to avoid sensitivity
from outside the glass.

The PIR half wont work through the glass so it shouldn't matter.

You probably want a PIR somewhere in the body of the house, such as
the main room or hallway, as door sensors are only perimeter detection
and don't cover the volume of the house accessed via other routes such
as broken window access.

When I worked at Chubb many many years ago we virtually never fitted stuff
to external doors, it was always on the internal doors and safes. The
exception being the exit route and shop windows where we fitted the lead
strips or break glass detectors.
the theory was that you wanted to catch burglars in the property not scare
them away.
I think CCTV to catch them and a perimeter alarm to scare them is probably
the best these days.