[csn]

The way I see it, dummy cameras and real ones have exactly the same pre-crime effect: they both create a sense of security and add to the observed risk associated with committing a crime. With dummies you get really low cost (practically no maintenance) but lose the benefits if and when a crime actually happens. Still net positive, I think.

Like common locks, cameras only really prevent opportunistic crime. And for prevention, dummy is as good as the real deal as long as it's not widely known which is which.

[yabun]

Only if people don't know about the dummies, things tend toward zero sum with awareness of the situation.