Someone broke through the chain link fence last week, in broad daylight, while I was home, and didn't notice at the time.
I started thinking about what I could do about it, and it turns out the EA Unifi cameras have a new webhook feature. So now my cameras send a webhook to Home Assistant when someone crosses a virtual line, and it will trigger the siren. Since this is a line crossing event, not generic person detection, I can leave it armed 24/7, since nobody should be in that area at all.