I imagine deterring vandals is a major consideration.

As often advised on here, most important is physical security.
(door/gate locks, window locks, door/windows/gates/fences properly
maintained, security lighting, etc.)

For the alarm, there are probably two significant aspects.
Firstly, making it a visible deterrent with visible external
sounders with flashing LEDs so they stand out at night.
That combined with good physical security basically says it's
easier to go and break-in somewhere else, so don't bother here.

Cameras and recorders are now a lot cheaper. A notice saying 'you are
being recorded' with physical evidence of it being true might also be a
deterrent. It might encourage imntruders to burn the place down to
destroy recorded evidence of course, but casting doubt into even a
moronic brain might work.

Peter Scott