When I re-furb'ed my last house I fitted window switches to all
accessible windows and external doors, so didn't need to bother with
PIRs. The current house already has a "professionally installed" alarm
with PIRs and door contacts, but no window contacts.
I was going to replace the PIRs with (a large quantity of) window
switches but am having second thoughts because of the unsightly wiring.

SWMBO is concerned about staying with the PIRs because, if we set the
downstairs ones at night, of what happens if someone goes down for a
drink or a wander around in the night. How does everyone else cope with
this?

I'm wondering whether it's viable to set-up an external boundary around
the house using infra red or laser beams/detectors (above animal
height). Has anyone used this technique?