$40,000-$60,000 per year per square mile. How many gunshots per capita per year per square mile do need for that price to make sense as a way to spend tax dollars?
It is a tiny fraction of the cost of police patrols in probably any mid-sized metro area in the US, and an even tinier fraction of that cost in major metros.
On the other hand, a full police force can handle more than murder. This can't. That would be okay if murder was the function of a police force, but its really just another amongst many responsibilities of theirs.
I suppose it depends how much time it shaves off of investigations.
Furthermore, I'm assuming they're not putting these in the middle of a Kansas corn field. Three people got shot outside of my apartment last year, I imagine they're going to prioritize that area over the upper east side.