I would like to derive an audio alert from a PIR floodlight. To be more
specific: let's say I have the floodlight above a back window and
driven from a three-pin plug from inside. I would be happy to bring
additional cabling from the PIR.

Or maybe forget that floodlight (I have another outside fed from the
garage) and use an external low voltage PIR to feed an audio alert
and/or switch on a light (even low voltage). I doesn't have to be DIY;
off the shelf solutions welcome!

Just thinking ... I suppose there is nothing to stop me feeding 240V
back from the switched supply to the floodlight.

Rationale: I'm interested in being alerted about potential burglaries
/before/ they enter; a few nights ago I heard was awoken by burglars
attempting to force a window. I assume also, that an audion alert just
loud enough to be heard outside might be a deterrent.

I'm sort of reluctant to fit a proper alarm; many reasons, but the main
one is that they tend to elart you only after the burgulars have gained
entry.

TIA,

Jon C.