Here's a decent article because this happened in recent weeks (1). The numbers they cite there are 89% of alerts lead to no reports of gun crime and 86% lead to no crime reports at all.

All that being said, the metrics are horribly flawed because they assume police will actually investigate anything after dispatch and that the investigation will turn anything up. Believing that CPD is going to case a neighborhood looking for GSR and shell casings with a forensics team is a tall order. If there isn't someone bleeding out in the street there probably isn't going to be a police report filed.

And even that said - ShotSpotter is useless because it requires police to do their job to be useful. When Reddit is better at tracking gang violence than cops, no fancy audio forensics tool is going to help.

(1) https://www.npr.org/2024/02/15/1231394334/shotspotter-gunfir...

"Definitive evidence of shots fired" is a higher bar than shots actually being fired. I agree it's still very low though, especially since it means that at least 95% of the time responding to the call was a complete waste of time (= even if shots were fired, there was no evidence of crime).

> Chicago also ditched it recently I think.

Kind of. The mayor said he was shutting it down for not being effective. And then he went and renewed the contract until just after the DNC convention: https://chicago.suntimes.com/city-hall/2024/02/22/shotspotte...

My read is that they know it does work but they don’t want to continue to use it because statistically the “wrong” people are committing the crimes it’s tipping off.

I mean brass can be crazy hard to find, I'd bet if you did a geocaching experiment with brass picking a random spot within shotspotter's accuracy tolerances, you'd find the casing less than 50% of the time. Add in an hourly employee that is in no way motivated to find the casing and you'd prob drop to 10%.