$40,000-$60,000/sqmile/year is an extremely reasonable number. Chicago has 50+ officers per square mile, implying tens of patrolling officers per square mile; the fully loaded cost of a single police officer is six figures, with potentially explosive defined-benefit pensions and benefits just to make things fun.

Moreover, like in many big cities (read Peter Moskos _Cop In The Hood_ for details), the squad car patrol tactics used in Chicago do a terrible job of suppressing gun crime. Over a 24 hour period this holiday weekend, we had 25 gunshot injuries (god knows how many illegal firearms were discharged above and beyond that). The police can't be everywhere, and the patrol process keeps them mostly in rolling squad cars.

And obviously, the overwhelming majority of gun crime in the city of Chicago are concentrated in a small percentage of our square miles: Austin, Garfield Park, and (particularly) Englewood and Chatham. Which makes systems like this cost-effective to roll out, and, particularly, easy to pilot.

I do have concerns about the use of conversations the microphones overhear but I know that in many neighborhoods events are not called in because the neighbor doesn't want the repercussions of turning in the local gang lord or his troops.

So, they could record conversations, but they won't for the time being. A classic example of using software to temporarily cripple the true capabilities of a computing device.

In the hands of DRM-wielding corporations, "defective by design" results in inconvenience and loss of users' freedom. In the hands of the surveillance state, the same technique results in a situation where citizens must simply trust the authorities to exercise restraint. Because the police could flip a switch at any time and record all sorts of conversations. Somehow I don't trust that the switch will remain un-flipped for long. And when it does get flipped, as it did in New Bedford, everyone will say it was just an accident.

Maybe, just maybe, we should accept systems like this as a necessary evil in certain cities where there's a lot of gun violence. Still, I don't like this. When it comes to the government, I'd much rather give them hardware that can't be unlocked "by accident" because there's nothing to unlock. The thing is, it's unrealistic to do that in all cases, and we have to hit a balance somewhere. Which is exactly why systems like this raise difficult issues.

Libertarians consistently make slippery-slope arguments when most everybody else is just happy that some immediate problem is solved. This line of debate is freaking getting old, and I'm the first person to do it.

The problem is that it always is a slippery slope. No bullshit. Changes take place over years or decades, so there's no single time you can raise an alarm. Right now it's gunshots. Next it will be car sounds -- estimating speeders and the conditions for traffic accidents. Then somebody will work out screaming. Then, perhaps conversations. And let's not forget that the systems will be justified by talking about the horrendous inner city. In actuality the vast majority of the time these systems will be used in places nowhere like that. When you read stories like this remember that these guys are selling equipment just like any other startup. You're getting their best pitch.

Big cities need this stuff, so it's a good thing for them. (Although I imagine we'll just start seeing a lot of silencers). What concerns me is that 90%+ of the time there's no crime being committed, save for discharging a firearm. So there's all these thousands of "criminals" discharging firearms that haven't been arrested before but could be now. Yay? Is it always a good thing with the grip of the state tightens, as long as we can point to something good coming of it?

Hopefully the cops will be so overloaded with gunshots they'll ignore the system and use it only for forensic purposes. But I doubt it. Instead I imagine we'll see these discharge numbers added to the crime reports for cities in an effort to secure more funding for even more police presence. Whether that's a good thing or not is debatable. There's obviously a real problem in Chicago and several other cities, but the rest of the country not so much.

Here's something from India. From times when weapons had to be carried secretly. https://en.wikipedia.org/wiki/Urumi

My forecast is that in the long run, bystanders will get less damage. But real murders get harder to investigate as there will be no gunpowder residue. And crossbow is easier to manufacture by oneself than firearm and that makes murder weapon tracking harder.

Or maybe, they got sick of calling the cops and not having them come. If the gunshots are that common, it wouldn't be uncommon for the police to ignore the complaints as a high-crime district.

Now they can ignore the automated reports instead of the called-in ones.

I would imagine that a criminal could use a system like this to do a DOS of police presence and/or send them on a wild goose chase so they can commit a crime in another area. In other words they get police to scramble to 5th and Main and they have another team to break into a place a few miles away with a non-gunshot crime.

Also, as anyone who has experience with home or business alarm systems knows false alarms get to be a "boy who cried wolf" issue and you begin to not take them as seriously as you should.

That would probably be a good thing for a competitor to create: a shot detection system that's designed to address civil liberty concerns. I bet someone on HN could do it.

Isn't that a total elapsed time of 2 minutes, 55 seconds?

But I try to be pragmatic about it. Gunshots fired in urban areas are one thing that really is the business of the police! There's always some tension between law and order versus liberty; the trick is to find ways to trade the latter for the former at as high an exchange rate as possible. This system strikes me as having a very good exchange rate indeed.

It seems expensive.

This technology also happens to be very useful for domestic counter-insurgence, something of interest to an economically polarized state during a time of economic transformation.

You could have one in every neighborhood. It might also be good in parking lots/garages.

EDIT: C'mon, downvotes? You do realize that vandalism will be a serious problem for this system.

The real concern will be when governments start to identify their citizens by their voice signatures, and then use that to track their whereabouts.

On the growth of such systems: it is almost inevitable that sensors end up getting placed everywhere. You have hundreds of sensors in your phone right now, many of them are uploading data to websites at various times.

Sensors will be placed on almost every utility as a matter of safety and efficiency. It is important to know when a pipe breaks or if there is a small leak in a gas main. Look up any given utility company and they will probably have some "smart" this or "integrated" that scheme in development.

There are cameras everywhere in most cities now, it is a matter of time before there are microphones too. Identifying who is where and who is speaking is a programming problem that has mostly already been solved. The two will be put together in the interests of safety and fighting crime. Someone might even invoke the terrorism word to speed up the process. Small-scale at first, in key places and important settings. Then rolled out across entire cities and states.

I am almost entirely visible to security cameras from the moment I step outside in the morning until I reach my office. Eventually, these systems will be integrated and process data effectively. The question is, what happens then?

You cannot come to reasonable conclusions about issues like this without seeing what's going on in the real world. This is not a math problem we're talking about; you can't sit around thinking and extrapolating and expect your conclusions to mean anything. It's like trying to run a scientific experiment without any data.

Do you know anything about criminal law? Do you know anything about the legal checks that are in place that prevent your doomsday scenario from happening? Are you aware of how evidence rules are applied in real cases? I'm sure you've read stories about the most egregious abuses, because they are the ones that pop up in the feeds that you read, but do you extrapolate from these that all cases are like this?

I say all this because I recently had the very eye-opening experience of serving on a juror in a five-week criminal trial. I realized that many of the prejudices that the technorati crowd has about the justice system are totally unfounded, at least for the case that I sat on. Our jury was not a clueless bunch of simpletons, our prosecutor couldn't get whatever he wanted by just saying "think of the children," and the judge was not an apathetic overworked bureaucrat who let anything slide.

What concerns me is that 90%+ of the time there's no crime being committed, save for discharging a firearm. So there's all these thousands of "criminals" discharging firearms that haven't been arrested before but could be now. Yay?

Are you really arguing that discharging firearms is a victimless crime? (edit: I'm talking about dense urban areas).

I wouldn't bet on this. Suppressors are highly controlled Federally, and completely illegal to own in Illinois (and Iowa and Michigan and a number of other states as well). You may think that doesn't matter to criminals, but most illegal firearms are purchased legally at some point-- not gonna happen for suppressors. And they aren't mix-and-match; you need a threaded barrel for your gun specifically. (There's a nice little scene in Goodfellas about this problem.)

But let's say you get ahold of one. You've got a line with a crooked Class 3 dealer in Indiana (this is someone who is also allowed to sell machine guns and grenade launchers) and he decides he's gonna risk his life by selling to a gang banger. Fair enough. So you get home, you load up your 9mm, screw on your shiny new suppressor, and go outside to take a potshot at some asshole you got beef with. Two minutes later, a couple of squad cars show up, lights flashing.

What happened? Well, you got your suppressor, but you're still using your same old bog-standard black-market ammunition. The can turns the hearing-damaging bang of your gun into a merely very loud bang, but it does nothing about the supersonic crack your bullet makes. You were quieter, but far from quiet; a ShotSpotter that was close enough easily picked you out.

If your dealer was looking out for you, he would have mentioned this, and recommended you switch to a subsonic ammunition. If he was really looking out for you, he'd also mention that this ammunition has significantly reduced range and stopping power, and probably does not have enough operating pressure to reliably cycle your automatic-- meaning you need to cock your gun every other shot like Jack Bauer. Sounds pretty much ideal for your inner-city gang fight, right?

And lest we forget, when the fuzz finally catches up to you, whether with the ShotSpotter or with good-old-fashioned police work, you are not going to get slapped with possession and sent upstate. As soon as that suppressor gets entered into evidence, with its nicely filed-down serial number, they're going to make a phone call, and the ATF is going to come to town with some serious Federal prosecution heat. They will hang you up by your toes until you tell them who sold the thing to you, and then they will find that person and make them severely wish that they had not.

So... yeah. Don't bet on it.

A more enlightened approach would be to ask why Chicago has so much trouble with gun crime, given that many other American cities have higher per-capita rates of firearm ownership both legal and otherwise.

One thing's absolutely certain: the real problem, whatever it is, will not be solved with digital signal processing.

If criminals want to use gunshot noise to scramble police presence to a specific area, they can obviously do that without gunshot detectors. The point of detectors is to make it easier to follow up on ideopathic gunshots.

However, it would probably be more effort than it would be worth, so it is probably more a sci-fi / crime plot than a scenario that is likely to come up often.