Detecting Gunshots

Minneapolis -- the city I live in -- has an acoustic system that automatically detects and locates gunshots. It's been in place for a year and a half.

The main system being considered by Minneapolis is called ShotSpotter. It could cost up to $350,000, and some community groups are hoping to pitch in.

That seems like a bargain to me.

Recently, I was asked about this system on Winnipeg radio. Actually, I kind of like it. I like it because it's finely tuned to one particular problem: detecting gunfire. It doesn't record everything. It doesn't invade privacy. If there's no gunfire, it's silent. But if there is a gunshot, it figures out the location of the noise and automatically tells police.

From a privacy and liberties perspective, it's a good system. Now all that has to be demonstrated is that it's cost effective.

Posted on March 20, 2008 at 7:27 AM • 74 Comments

Comments

Max StirlitzMarch 20, 2008 7:51 AM

In the Deus Ex game, there were these kinds of sensors in the Hong Kong part of the game...

Complete with fake news articles about them and their cost-effectivness.

Like the fall of the WTC*, Deus Ex is a tad predictive :)

Though I hope no one'll unleash any kind of nanotechnological plague as in the game.

*they didn't fit onto a texture, so were left out and their absence from NY skyline was explained by terrorist attack. In '99.

Nick LancasterMarch 20, 2008 8:00 AM

San Francisco just implemented a gunshot detector in the Bayview-Hunters' Point area, which is gang turf. Other Bay Area cities have been using this for several years.

Kevin D. S.March 20, 2008 8:53 AM

One minor concern would be an organized group of ne'er-do-wells using the technology to draw law enforcement away from the area of an actual crime. Likelihood? Probably low.

MichaelMarch 20, 2008 8:53 AM

How well this works depends on how the police react. If it leads to a reasonable investigation, then it's a good idea. Unfortunately, I see the police showing up at a home, handcuffing all the residents, searching the house, and confiscating any guns they find, regardless of what may have actually happened.

chris jMarch 20, 2008 9:00 AM

@Kevin D. I thought the same thing, and that there will be a rise in stabbings.

First thought: It can detect gun shots, how can I use this to my advantage?

chris jMarch 20, 2008 9:02 AM

not being a gun owner, can the system tell the difference between a gun shot and a firework? What about a car backfire (those are rare these days).

AndyMarch 20, 2008 9:06 AM

So this will now drive criminals to use silencers? On their web site they say less than 1% of all crimes in which guns are fired involve silencers and they're illegal nationwide!

IanMarch 20, 2008 9:11 AM

Several Problems with this.

1. Dirt Bag X will discharge his/her fire arm next to rival Dirt Bag Y’s grow op/gang house to draw police into that area.
2. Unless there is a clearly defined scope of investigation from gunshot detection, the Police could use this excuse to conduct spot checks on all individuals in a given radius because a gunshot was detected. If they find a bag of weed on you but no fire arm your still going to jail for being in the wrong place at the right gunshot time.
3. See above, Police could actually trigger the system in order to conduct a search of a suspect’s residence, vehicle, or individual because they now have “reasonable cause” due to the gunshot detection
4. Criminals will use silencers or small calibre weapons (.22 for instance) instead of things that go bang loudly.
5. And as previously mentioned, stabbings and beatings will be used to achieve criminal ends just as effectively as the use of fire arms.

My .02

Kevin D. S.March 20, 2008 9:12 AM

@chris j

Caveat: My thoughts might be a bit toward the "movie plot" arena...

First - as I understand from the article, the sensors pick up the sound of the gunshot.

So, I could have fun one of two ways:

1) Network (wireless) a few lowprice laptops with decent speakers around a localized area and at a given time begin a sequence of "gunshots' that would simulate a large "gangfight."

2) I could employ a group of people to fire (at no particular person) to make the "noise."

Each option has its own advantages and disadvantages. However, while the police are focused in another area, I could execute some type of crime where police response time is critical (i.e. bank robbery).

Movie plot? Probably.

MikeMarch 20, 2008 9:15 AM

"From a privacy and liberties perspective, it's a good system."

Unless (or until) it is integrated with neighborhood anti-crime cameras. That hypothetical combination has the potential to detect, photograph and identify the shooter. The possibility of a false ID with that combination is real, yet likely will be discounted by the justice system. Many guilty will be caught. A few innocent will be too.

spongeworthyMarch 20, 2008 9:20 AM

OK, so now you know when and where a gun has been fired. Then what happens? You may know when and where the shot was fired but you don't know who did it or why. Do you dispatch patrol cars and, if so, what do they do when they get there, especially if there's no victim? Do you expect whoever fired the weapon to hang around waiting for the police to arrive?

If I was a smart criminal (oxymoron?), I suppose I could instigate a DOS by having associates fire guns to pull the police out of position protecting valuable assets.

I guess I just don't understand the benefit of knowing when and where a weapon was fired, especially at such a cost.

scottMarch 20, 2008 9:25 AM

@Ian

If criminals are going to react to the system - it just means it's working; it's putting pressure on them.

The basic principle is sound and this system just automates a pre-existing process: when people hear gunfire, they call the police.

1) Is causing a disturbance worth the risk of being seen firing a gun on enemy turf? This won't happen because it will always be easier to leave an anonymous tip via phone.

2)This says nothing about the system - everything about what laws are put in place behind it.

3)As with 1) I suspect that there are easier ways for police to abuse the system than shooting the place up.

4)This just shows that you're making a previously easy task (any old gun will do) more difficult for criminals. How is this a bad thing?

5)As with 4), stabbings and beatings are not as effective as firearms. Why do you think criminals adopted the use of firearms in the first place?

TSMarch 20, 2008 9:25 AM

@Chris J

Even by ear you can easily tell the difference, you can even tell the difference between different caliber weapons, they all sound a little different. I would guess that the signatures are significantly different so the computer doesn't have a difficult time differentiating them. I wonder how good they are, if they can tell the specific caliber or type of weapon?

Oh yeah, fireworks are illegal too, might be good to send some cops to the location, although it's not a priority.

HawkinsMarch 20, 2008 9:34 AM

SpotShotter?

Man, that's a dumb name. Sounds like a stain removal device. Wouldn't ShotSpotter be more appropriate?

Maybe it was taken.

RoyMarch 20, 2008 9:46 AM

Suppose the gadget gave the location as the center of an intersection in a residential neighborhood. Would the police use this as carte blanche to forcibly enter any home of their choosing? Then could imprison all occupants and search everyone and everything, seizing all firearms, all without warrants. Failing to find a freshly fired gun -- the failure of their telltale -- they could use the same 'determination' to invade the next home, and the next, and the next, and the next.

This will be yet another witness against the accused that does an end run around the 6th Amendment.

What happens if I drive through your neighborhood and fire a gun out my window and then hurry away to watch the fun? I could count on the police to always do the wrong thing.

mashiaraMarch 20, 2008 9:50 AM

Explosives (simplifying by mixing propellants like gunpowder to same class) have very distinct acoustic signatures, also: recording the *real* sound of an explosion isn't exactly easy.

I do some SFX work and there is no point at all in trying to record the sound of explosions, the microphones used for normal audio simply cannot handle it (we do measurements with high-speed pressure sensors sometimes, but the pressure graph doesn't readily translate to anything that would sound cool)

I don't think there exists a speaker system that could accurately emit something close enough to the original sound of a gunshot, and in any case it's not a system you would leave laying around...

What a person hears from one is mixed with lots of reflections from the ground and anything around it, also humans have limited "sampling rate" (which is why locating sound underwater is so much harder, sound travels so much faster there than in air and thus the time difference between sound reaching left an right ear is much smaller)

MikeMarch 20, 2008 10:01 AM

Most of the above objections assume that the police will make various mistakes, or will violate constitutional rights, or that the criminals will find a way around the system. These are not objections against the system itself.

It's like objecting to dna forensics, on the grounds that the police will ignore all other evidence, or that a criminal will plant dna to frame someone. These are not valid objections because they are outside the system being considered.

It's like objecting to the design of a new more secure door lock by saying that criminals will just use the windows.

derfMarch 20, 2008 10:06 AM

How exact is the sensor? Can it tell the difference between weapon types? Can it tell the difference between an actual gunshot and say a plastic bottle or an electric transformer exploding? Are false alarms on these things going to cause it to be ignored or put on the bottom of the priority list like home burglar alarms are now? Doesn't this seem kind of pricey for something that has a rather decent chance of just being ignored?

Questions, questions, questions.

RogMarch 20, 2008 10:08 AM

@Hawkins

It looks from the links on original site that "SpotShotter" is a typo in the story and that the product is actually called "ShotSpotter".

DanielMarch 20, 2008 10:12 AM

The rising use of technology to battle the symptoms doesn't help to cure the root of the problems:
- firearms for everyone
- education
- extreme differences in income
- ...

DaveAronsonMarch 20, 2008 10:24 AM

@Andy: Silencers are not illegal, just heavily regulated and taxed. (I'm assuming you mean in the USA.)

@Ian: They won't use .22s if they want the other guy stopped within a reasonable amount of time. .22s kill more people than any other caliber (as of several years ago; dunno if still true), but as the saying goes, they don't fall down then and there, they get mad, hurt you, and die three days later of peritonitis.

@TS: Whether fireworks are illegal depends on where you live. Setting them off in a normal public area, probably illegal in most places (my guess). So you're kinda right, but there may be sensors close enough to fireworks-OK places, that they cause a DOS. Wonder what happens on July 4?

@Mike: These other things do need to be considered. To use your analogy, someone might comment: "Before you spent $1,000 on this fancy lock for your front door, maybe you should start closing or barring your ground-level windows, which I notice are wide open."

AnonymousMarch 20, 2008 10:24 AM

@Mike

"Most of the above objections assume that the police will make various mistakes, or will violate constitutional rights, or that the criminals will find a way around the system. These are not objections against the system itself."

Nonsense. If a system makes it easier to abuse the rights of people, then that is a system problem.

alanMarch 20, 2008 10:26 AM

I wonder what the detector will do on Chinese New Year with all the firecrackers going off?

RoxanneMarch 20, 2008 10:54 AM

I think that it will be modified to detect other sounds that they don't like; perhaps screams, or skidding automobiles. In the meantime, it means that gun users will develop better silencers (yeah, they're illegal - so is the gun) and kids will develop other sounds to trip the sensors, just because.

I don't like people listening any more than I like them watching.

AnonymousMarch 20, 2008 10:58 AM

There was a show on Comcast, one of the HD channels like Discovery HD or something, about technologies, particularly less-than-lethal ones, being tested and in some cases used by Law Enforcement around the U.S. The show was filmed with the LAPD or LASO, and they showed the ShotSpotter system in place in LA.

It was a very good, focused solution for a single problem. All of you complaining about how this can be abused by police or malicious/mischievious individuals are missing the point. The technology is valid and useful; how it is used and implemented by government is the problem you describe, and frankly doesn't merit much attention here.

Sorry, not intending to troll/flamebait, but I get tired of that crap. As a former police officer, I can appreciate how this would make responding to "shots fired, no further information" calls quicker and more effective. I also appreciate how every 'group' has it's bell curve. You have cops and gov't officials at the top 10% of the group and those at the bottom 10%. It's a human problem. Deal with it.

BrianMarch 20, 2008 11:05 AM

In Columbus, Ohio, wasn't this technology was used to try to zero in on the suspect in 2003, when someone was randomly and sporadically shooting people on I-270 on the south side of town? I remember that they installed the devices, but I can't remember what the actual results were.

AMarch 20, 2008 11:11 AM

The military was trying some of these out in Iraq when I was there a few years ago. We shut them off after the first use because they had so many false positives (and the system was only trying to give you a general direction, not a location within 10 feet).

Granted, they were installed on a moving truck that was speeding down a bumpy road, so it probably made the problem that much harder.

AnonymousMarch 20, 2008 11:21 AM

@ Anonymous (aka. Mr. Deal with It)

I can understand your perspective and I have a bit of kindly-offered advice. (No sarcasm or spite intended).

If you are looking for a "does it work" discussion, then perhaps you should look elsewhere - perhaps IEEE or Consumer Reports.

If you are looking for a discussion of the unintended consequences of well-intentioned technologies (and many other discussions at the intersection of security, privacy, technology, psychology and economics) then you are in the right place.

Save yourself the frustration and find the right place to be.

Alan KruegerMarch 20, 2008 11:40 AM

While this is useful, urban areas might call for something carried by individuals to help deter muggings and the like.

A tazer or other defensive weapon that, when triggered, electronically broadcast requests for help until it ran out of battery power. This could act as a black box, making GPS and audiovisual recordings to identify the perpetrator after the fact. Since it would continue broadcasting for help, the perp couldn't just run off with it or hope to hide it, it would continue summoning the police to its location. You could tell where the crime occurred, who did what, and what happened afterward.

Being able to react to gunshots in the city sounds useful, but that doesn't help when one is simply menaced by a gun, or if someone uses a knife.

SteveJMarch 20, 2008 12:04 PM

@Ian:

"1. Dirt Bag X will discharge his/her fire arm next to rival Dirt Bag Y’s grow op/gang house to draw police into that area."

They can do this already. If you stand outside Dirt Bag Y's house and repeatedly fire into the air, *someone* will notice eventually and might even call the cops. This system detects single gunshots, so, OK, it saves Dirt Bag X a few rounds, but it also detects crimes involving only a single gunshot.

Also: so what? Criminals can phone in anonymous tips about each other's offences. Are you saying that's somehow an argument *against* the police answering the phone?

"3. Police could actually trigger the system in order to conduct a search"

They can do this already, just like Dirt Bag X can. If the police want to fake up some suspicious gunfire and then march in, they don't need an automatic sensor to do that. The measures currently in place to attempt to prevent the police doing that, will still work with the sensor. No change.

" 4. Criminals will use silencers"

Not much - it's hard to make a good silencer, it's dangerous to use a bad one, and they're somewhat difficult to buy. In fact, if all this system did was ensure that if you want to use a gun in a crime, you have to get a silencer, then that's a win, and probably worth it at the price quoted. You force them to commit an offence, and you have some chance of catching them, *before* they even get to the point of shooting anyone. And at no cost to civil liberties, since silencers are already mostly illegal.

" 5. And as previously mentioned, stabbings and beatings will be used to achieve criminal ends just as effectively"

No: if they were "just as effective", criminals wouldn't be using guns now. They are in fact somewhat less effective. Despite living in the generally anti-gun UK, I personally think that private ownership of guns should be permitted. So if this scheme did somehow cause criminals to stick to knives and fists, personally I'd consider that a *massive* win, and well worth the price.

I know you intend your point as a criticism, and I wish it were true, but it's not. What will actually happen is that criminals will carry on using guns, and the police will find it a little bit easier to catch them when they do.

justinMarch 20, 2008 12:15 PM

As another Minneapolitan, my understanding of this system is that it has been working quite well. The city even puts their shots fired maps on the web: http://www.ci.minneapolis.mn.us/police/crime-statistics/codefor/shotsfired.asp

Interesting things that I've heard in Minneapolis: Potential shooters are aware of the system so it's a deterrent. Also, our city-wide wireless system confuses the would be shooters who can't tell the difference between the shotspotter boxes and the wifi boxes.

The Wired article Jason linked is quite good and does a great job of summing up the system. I consider it tax dollars well spent.

AaronMarch 20, 2008 12:19 PM

Frankly, gangs relying on knives is vastly preferable to guns.

I doubt in the history of human violence there has ever been an instance where someone drove by a house and started throwing knives out the window and accidentally hit a little girl.

Personally, I don't really care if they kill each other off, and taking away their ability to use guns limits their violence to being more directed and less likely to hit bystanders.

jdegeMarch 20, 2008 12:34 PM

Actually, I think these things may cut down on false positives. In my experience, most people can't tell the difference between the sound of gunfire and the sound of firecrackers. Not surprising if your experience with firearms is only from movies, TV, and video games.

My guess is that most of the reports of "shots fired" in Minneapolis are nothing of the sort.

Could the dispatchers use the system to filter out false alarms? I don't know, depends upon the design. But it'd be a useful capability.

DenseMarch 20, 2008 12:35 PM

At the risk of sounding dense: I'm not sure I get it.

So this system automates the detection and locating of possible gunfire. For multiple hundreds of thousands of dollars. It might even work, but what exactly is the benefit? I'm not arguing that there isn't any, but that it has not been made clear.

Bruce, you say you like it, because it's not bad. But is it good?

AnonymousMarch 20, 2008 12:53 PM

@justin

"The Wired article Jason linked is quite good and does a great job of summing up the system. I consider it tax dollars well spent."

Well, that article has two apparent false alarms out of three listed encounters. Exactly how many false alarms -- cop arrives and finds nothing -- are being logged?

AnonymousMarch 20, 2008 1:15 PM

How do you know they were false alarms? Absence of a threat upon scrutiny does not mean the theat wasn't there at the time it was recorded by a sensor.

AnonymousMarch 20, 2008 2:00 PM

"How do you know they were false alarms?"

How do you know they were _not_ false alarms? If you arrive in a room where a smoke detector has gone off, but there is no smoke, what do you call it? More generally:

P(threat|data) = P(data|threat)*P(threat)/P(data)

Insert whatever biases you wish and come to your own conclusion.

Now, are these systems carefully monitoring this stuff, or is this all just "well golly gee, write ShotSpotter another check 'cuz all those red-dots are just sooo useful for scaring the citizens!"

justinMarch 20, 2008 3:04 PM

So what if the false alarm rate is high?

This is an entirely different animal than false alarms in facial recognition, for instance. If you get a false alarm and dispatch sends a squad to the corner of 5th and Vine and nobody is around, is there real harm in that? Nope. The police just move on and respond to another call.

Police departments usually have squads cruising around anyway, and given the relatively few spots that happen, even if they investigate all of them (and I hope they do), I'd consider it a good use of time. Seems to me like the benefits outweigh any downside. The

AnonymousMarch 20, 2008 3:04 PM

@Portico

You do realize that the biggest threat to yourself, friends and other members of your family are -- how to put this delicately? -- yourself, friends and other members of your family?

http://malini.data360.org/graph_group.aspx?Graph_Group_Id=1177

(Australian data, but the conclusion is global and well known to cops everywhere.)

But hey, don't let a few little facts get in the way of the world of fear!

AnonymousMarch 20, 2008 3:27 PM

@justin

"If you get a false alarm and dispatch sends a squad to the corner of 5th and Vine and nobody is around, is there real harm in that?"

Well then, I can save the people of Minneapolis half a million bucks: for no fee whatsoever I'll write them a simple computer program that randomly generates street intersections and presents them to the 911 dispatchers as "shots fired". Send out a car, have them fill in paper work, move on to the next domestic.

Bruce SchneierMarch 20, 2008 3:50 PM

"So this system automates the detection and locating of possible gunfire. For multiple hundreds of thousands of dollars. It might even work, but what exactly is the benefit? I'm not arguing that there isn't any, but that it has not been made clear. Bruce, you say you like it, because it's not bad. But is it good?"

It depends. If the police need to dispatch officers to the location of gunfire quickly, this kind of system is likely to speed up that process. It also could help in reconstructing crimes -- location, time, etc -- and so on. I don't know the details, but my guess is that this is valuable.

RoyMarch 20, 2008 3:54 PM

I'm not surprised that the public is little help with gunshots.

I once lived in the middle of a small city. Late one night I heard two shots fired close by and dutifully (read 'stupidly') called the police, giving the location, the interval between shots, and reporting that it sounded like the same gun fired twice. I described the sounds as a small-bore centerfire handgun, either a .25 or a .32. The dispatcher assured me I'd only heard a car backfire.

The next morning I found two fresh .25 ACP cartridges laying on the street. I called the PD to correct their 'correction'. That got me on their shit list.

Gun NutMarch 20, 2008 4:34 PM

> Recently, I was asked about this system on Winnipeg radio.
> Actually, I kind of like it. ...
> From a privacy and liberties perspective, it's a good system.
> Now all that has to be demonstrated is that it's cost effective.

Just out of curiosity, what are your views on gun control? I'm just wondering if your opinion of _this_ system may be a bit biased (or not).

Tangerine BlueMarch 20, 2008 7:49 PM

@Gun Nut

> I'm just wondering if your opinion ...
> may be a bit biased (or not).

What difference do his views on gun control make? I'm sort of an NRA guy - I think the 2nd amendment guarantees individuals the right to have a gun. But if somebody is shooting guns in the WalMart parking lot, I think the police ought to check it out.

wMarch 21, 2008 7:43 AM

Seems like vendor welfare to me. The purpose of these systems were to triangulate weapons fire in unihabited or hostile areas. Minneapolis wasn't in a state of insurrection the last time I checked the news.

I'm going to assume there is still 911 available in Minneapolis. When there's a criminal shooting, there's going to be a flurry of calls. Not only will these calls give equally decent triangulation to answer the "where" question, they're going to provide essential context around the event.

These kinds of systems will now duplicate the "where" portion of the response process. How much value does that add?

Consider the situation where the system reports gunfire, but there is no corresponding context provided through 911 calls. Is it a false positive? How many resources do you respond with? Do you need the SWAT team, or can you just send one unit?

Spending that money on equipment and extra personnel to operate it (and maintenance contracts, and all the rest of the scam) inevitably leads to a policy where the technology triggers a mandatory response to justify its expense. Taxpayers are going to suffer the extra expense of over responding to false alarms or minor situations, while the police are going to deal with situations where a single unit is dispatched into potentially dangerous situations because not enough shots were detected to trigger the next level of response.

AlbionMarch 21, 2008 8:31 AM

I like this idea. I have considered this in the past, and most of my earlier thoughts have been touched on in prior posts.

I like the threat that firing a defensive handgun can attract police presence. This makes a warning shot, actually usefull.

I like the possibility that a tie in to surveilance systems could direct attention to the event. This has a multiplier effect on existing surveilance investment.

This type of system if cheap enough would be also be usefull for monitoring hunting areas for poaching, or other game violations.

There are several countermeasures available such as silencers (difficulties already discussed), subsonic loads (might introduce legal limits on handloading), compressed air guns (good ones are as effective as firearms), alternate weaponse such as crossbows, knives, clubs, etc. But guns are already plentiful and cheap, so they are already a significant social risk which wold benefit from controls if the cost is acceptable.

It is often better to put controls on the use of a technology, than trying to prohibit it.

Albion.

SteveMarch 22, 2008 10:57 AM

@DaveAronson said "Silencers are not illegal, just heavily regulated and taxed. (I'm assuming you mean in the USA.)"

Wrong. Silencers are highly illegal, try checking the law before you past such nonsense.

http://www.atf.treas.gov - here's the law from my state that defines a "weapon of mass destruction":
"...
(3) ... any muffler or silencer for any firearm, whether or not such fire-arm is included within this definition. "

David TerrellMarch 22, 2008 11:25 AM

Uh, seriously, how many of you people actually live in an area where people get shot on a regular basis? It is very difficult to get people to recognize what direction shots are coming from, or even to report them at all.

dude-from-gangtownMarch 22, 2008 8:55 PM

I am with Bruce in that I like the concept. While I am concerned about possible police abuse, the risk is minimal. The real risk is with the false alarms, which could result in someone dying because cops were responding to a "gunshot" that never occurred.

As for silencers, you can know they are illegal with one fact: I don't have one. If they were legal, I'd have one. Quite useful.

@David
Two years ago, I lived on a street that made the news for number of shootings. We had holes in the house, and I slept by the shotgun near garage so I could hear attempts at theft. To answer your question: yes, I know where gunshots come from.

If houses aren't too close together, we can usually point out the house it came from (error range: 1 or 2 houses), so long as we know the type of gun by the noise. I don't see why folks have so much trouble with that, as my ears aren't even all that good.

Finally: I *will* be screwing around with this system if we get one. I just don't think it will be too useful. Most shootings are drive-by's, and they are gone in seconds.

country boyMarch 22, 2008 8:56 PM

I am with Bruce in that I like the concept. While I am concerned about possible police abuse, the risk is minimal. The real risk is with the false alarms, which could result in someone dying because cops were responding to a "gunshot" that never occurred.

As for silencers, you can know they are illegal with one fact: I don't have one. If they were legal, I'd have one. Quite useful.

@David
Two years ago, I lived on a street that made the news for number of shootings. We had holes in the house, and I slept by the shotgun near garage so I could hear attempts at theft. To answer your question: yes, I know where gunshots come from.

If houses aren't too close together, we can usually point out the house it came from (error range: 1 or 2 houses), so long as we know the type of gun by the noise. I don't see why folks have so much trouble with that, as my ears aren't even all that good.

Finally: I *will* be screwing around with this system if we get one. I just don't think it will be too useful. Most shootings are drive-by's, and they are gone in seconds.

TruePathMarch 23, 2008 2:34 AM

I find it ironic that in a discussion about the potential unintended negative effects from technology the critics of this program are mostly acting as if oppossing programs because it is conceivable that the police might use them as an excuse to invade privacy/violate civil rights doesn't itself run the risk of unintended consequences.

For starters the idea that we should simply evaluate something's effect on civil liberties/privacy by examining how likely it is to be misused is simply wrongheaded. You can't evaluate a law enforcement tool in a vaccuum, you need to compare it to other tools already in use that it is likely to replace. Since anonymous tips are one of the most abused tools the police possess to the extent that shotspotter tips occupy police time that would have otherwise gone to investigating anonymous tips or other abuse prone methods it's a net win on privacy and civil liberties.

Moreover, one has to ask why cops violate privacy and civil liberties. Sometimes it's just corruption or lack of morales but I think mostly it's because the cops are frustrated by the hoops they must jump throw to get someone they 'know' is a 'bad guy.' To the extent this is true the more investigative tools you put in the hands of police the less abuse you should expect to see. At the very least this is a possibility that should be considered.

Finally, I would argue that oppossing these technologies for the reasons given here is actually another significant contributor to police abuses. This system simply gives the police the time and location at which a crime took place (firing a gun inside city limits in big cities in most circumstances). At the very least oppossing this on privacy grounds without a much more specific concern gives the impression that any improvement in police technique would be similarly oppossed (gives them more info). This may not be true but I think trying to opposse this sort of system gives that impression and thus discourages the law and order crowd from listening to more serious privacy and civil liberties concerns for other techniques.

I think they really ought to use these systems to take a picture of the location of a gunshot when it occurs (and only then). This would actually protect against many of the potential abuses (less guessing about who fired it...more deterence) without much drawback that I can see.

-----

Then again I really don't see the harm in having our public actions recorded, i.e., lossing our obscurity, so long as everyone loses it equally. We lived this way for thousands of years in small villages where everyone knew each other's buisness and we will live just fine that way in the future. In fact I think it might actually lead to a better world. After all most of the harms from the loss of obscurity come from the worry that stupid shit you do will get back to your boss/government/etc.. However, in a society where everyone's stupid shit is public the impact will be much less.

Besides, we might as well give into the idea of being monitored in public since obscurity is on a collision course with free speech and technology. Unless you want to impose draconian controls on people's personal cameras soon we will start wearing little video camers to help remember faces and events. Some people will post this info to the internet and computer vision algorithms will let people search for the data and extract info. Rather than worrying about whether we should have microphones and cameras in our cities we should be worrying about whether they are going to be deployed equally in rich and poor areas. If only the poor are monitored then we need to worry.

A NameMarch 23, 2008 3:35 AM

> > I'm just wondering if your opinion ...
> may be a bit biased (or not).

>What difference do his views on gun control >make? I'm sort of an NRA guy - I think the >2nd amendment guarantees individuals the >right to have a gun. But if somebody is >shooting guns in the WalMart parking lot, I >think the police ought to check it out.

I think his political views do make a difference. Bruce doesn't seem to think much of gun rights and doesn't seem to use the same logic in discussing security related to firearms. He opposed arming pilots after 9/11 at a time when there were no reinforced doors on the cockpit and internal tests showed that airport security was letting 25% of hidden firearms onto airplanes.

I agree with Bruce most of the time but whenever the topic has anything to do with guns I question his opinion. I suspect he is not a pro-gun rights guy.

KanlyMarch 23, 2008 4:44 AM

> In my experience, most people can't tell the difference between the sound of gunfire and the sound of firecrackers.

No, but the software that processes the audio stream could. $350K? Pretty cheap really. All you need is an embedded system, audio input, some sort of comms system. Factor in the cost of writing the software (which doesn't have to do that much), installing and maintaining the system. Not bad. At the moment if someone reports a gunshot it's real vague.

Doug CoulterMarch 23, 2008 6:04 PM

I am a recently retired digital signal processing consultant, and am currently a gunsmith, so I suppose I can fill in some facts for this discussion.

But opinion/politics first:
I think the emphasis on possible misuses/abuses of this kind of system is (very sadly) completely well founded, and backed up by publicized actual occurrences of abuse. Police have, in my opinion, far too much discretionary power, and have lately begun to abuse it more and more. In my small town, this is not a very big deal, where everyone knows everyone, and abuse is not rampant -- if a cop does something bad to a good citizen here, he won't last very long in his job.

Law enforcement has a much tougher problem in a dense population where everyone is a stranger, however, and grasp at whatever seems to work -- and that's the honest, caring ones. Having lived in both sorts of places, the differences are pretty obvious and well confirmed, at least by me. In my small town, it is against the law to go into public without ID AND at least $200 in cash, else one is a vagrant. It's something the cops keep in their back pockets if they want to look one over for awhile, in lockup and have nothing else to go with at the moment. Here it is even a felony to have some kinds of consensual sex acts with one's legal spouse(!) -- also just about never used -- but it could be.

Selective enforcement is a very dangerous thing to our rights in general. It lets politicians claim they are doing something and pass some very rights-threatening laws, and in the better cases where they aren't abused, prevents the huge backlash that would occur if those laws were enforced, say, as vigorously as even speeding on the roads, or public drunkenness, which many people regularly get away with. But as they are on the books, and largely unchallenged, this could change at any instant, at essentially the sole discretion of an officer, who in effect becomes judge and jury on the spot. I thought we had separated those functions for sufficiently good reasons!

As to the DSP of detecting gunshots, it's a relative piece of cake. Gunshots are characterized by a supersonic muzzle blast, followed by the usually supersonic bullet, both of which have risetimes not created by almost anything else. All this is followed by multipath echoes from which various parameters can be determined with pretty good accuracy. Our military has looked into this for their own uses, with success.
As taxpayers, we've paid for that already.

I agree that recording gunshots or explosions is tough, but it is still very do-able if one sets up for that.
I've done it, and used a gunshot for a snare drum sound in the recording studio. There are even records available of the sounds of cannon fire for Civil war re-enactors and historians, and they sound pretty realistic. What IS difficult is reproducing them with most current audio equipment.
The SPL is just so high that human perception is in a nonlinear mode (not to mention the air itself -- it can compress to almost any pressure, but not rarify below a vacuum), so a level that wouldn't cause legally actionable damage to listeners doesn't subjectively sound the same without a lot of compensations. I've heard it done well in a movie (Terminator) with one exception -- after the first shot inside an elevator, one's hearing would be severely affected, and subsequent shots would not sound the same.

What got much more interesting for my company was when we were tasked to do a "scream detector", which has a lot of the same system-gaming problems. This was for a customer who makes PA systems for schools, airports, and other security related equipment. In a classroom, especially elementary, students scream a lot, and it means nothing except a disciplinary problem -- and a wide open invitation to abuse such a system. So, it boiled down to "how to tell a real scream from a fake one?". Imagine figuring a way to take data on that without accidentally scaring someone to death or winding up in court! And not everyone screams when suddenly frightened. Sadly, the project never got past that obstacle, and I doubt one ever will, unless someone just takes data until real events occur enough times for a significant data base to be built. Obviously fake screams are easy to get data on by comparison. At least it was entertaining to think about how to truly scare someone without backlash -- but no solution eventuated.
I personally believe the detector could be done, but not without good data. Would have been fun, but...that's a really big but.

As a gunsmith, I can say that BATF class III devices, which include machine guns and silencers are legal, but it is so much hassle with paperwork and fees that only the very wealthy can get there from here. This is a federal law, carefully crafted to avoid running hard into the 2nd amendment, but still accomplish the severe reduction in availability of such things in general. It's about as hard as getting a very high level security clearance, but you do the paying for all expenses, rather than an employer, and there is no market competition for the costs. States may pass various laws, but face a test on pre-emptive restrictions if they get taken to court on them, in which cases they mostly fail. After a very expensive and time wasting bunch of legal wrangling.

Our gun club has a semi-annual machine gun shoot, well attended by law enforcement folks, for example, where one can rent time on various legally owned full auto guns. Fun, but it's expensive! Bottom line, these things can be legal, if you have a squeaky clean record, lots of patience, and tons of money to get the permit, then another ton of bucks to buy the device. This is one reason that you almost never hear about one being used in an actual crime if the reporting is at all accurate. They are just not common at all, and so are even hard to find to steal from someone who legally has one. Not many people want this kind of thing badly enough to handle the 6 figure total price, and the extensive waiting involved. Criminals lack money and patience, one reason we've also not seen crimes with .50 cal rifles -- they cost far too much to be in any way common, and to boot are darned difficult to move and disguise due to size and weight.
Walking around with one attracts a lot of attention, even at a gun show, as I noticed just yesterday.

The movies give a very false impression of the capabilities of silencers, by the way. They only really work for subsonic bullets, and guns with no other gas leaks, which eliminates all revolvers, and semiautomatic pistols that haven't been modified to be single shot by locking the slide closed. Due to aerodynamics, the bullet velocity must be well below the speed of sound at about 1130 fps -- more like 800 fps, or it gives the loud supersonic "crack" as the air has to move a little faster than the projectile to get out of the way of it. Revolvers and pistols leak, around the cylinder-barrel gap in the former case, or by unlocking during high pressure in the latter. It is still quite a bang, in short. So the TV/Movie "zip-zip-zip" is completely fake and never encountered in real life. There was some work in WWII with subsonic rifle rounds with very heavy bullets (so they'd still have enough energy, even if slow) by resistance fighters, but one had to be very close for that to work.
You'd be far better off with a crossbow.

Even in some Scandinavian countries where silencers are legal (and encouraged for hunting!) they don't work all that well, even though there is a market and therefore design impetus for continuous improvement. It's just really hard to make a good enough acoustic low pass filter to cut the blast down much more than a few 10's of dB, at least a portable one. And considering that you may be starting essentially "off the scale", cutting the blast down to say, 140-160dB absolute doesn't by any means make things "silent", "quiet" or anything but less-immediately damaging to the user's hearing.

Mr. SmithMarch 23, 2008 6:07 PM

@ A Name

I'm pro gun rights, but I also opposed arming pilots in the days immediately following 9/11. Pilots are there to fly the damn plane. This task cannot be delegated to anyone else on the plane.

If the cockpit needs defending, station an armed guard, air marshal, National Guard soldier, whatever in the cockpit or at the doors until you can reinforce the cockpit doors. And if you think the passengers wouldn't act as reinforcement for that lone guard, there is a crash site in Pennsylvania you should visit.

rai March 24, 2008 10:48 AM

I live on a corner with one of the shotspoter cans, it has not done much except caused police patrols to be down in a neighborhood where gunshots and firecrackers are not uncommon. Police in the twincities do not live in this part of town, they tend to live in a suburb called maple grove where they can get together and elect one of thier own to the state legislature and ensure that all matters in thier vested interest has a representitive who will bring his conflict of interest to bear.

Just WonderingMarch 24, 2008 6:46 PM

@Doug Coulter

"Gunshots are characterized by a supersonic muzzle blast, followed by the usually supersonic bullet, ..."

Shouldn't that be PRECEDED by a supersonic bullet? If the bullet is supersonic, then by definition it's traveling faster than the sound of its muzzle blast, right?

r00tbeerMarch 25, 2008 3:22 PM

Silencers aren't illegal in the United States. They are regulated under the National Firearms Act of 1934.

However, they are illegal in a few states.

Dick C. FlatlineMarch 26, 2008 10:02 AM

There is no such thing as a "silencer" (outside TV and novels). There *is* such a thing as a "suppressor" (which, again only in TV and novels, works efficiently when screwed onto the muzzle of a revolver). On *some* semiautomatic handguns, it *is* possible to temporarily fit a plastic bottle over the barrel and, "sealing" the junction with one's other hand---ALWAYS use a glove, campers---, sufficiently suppress the sound of the first discharge to be practical. (Subsequent rounds dramatically degrade the efficiency.)

So, yes, I'm all for the gunshot detection system, but only if we also deploy a vast network of cameras designed to detect Michael Jackson lookalikes carrying 1-liter soda bottles.

spirit equalityNovember 18, 2009 1:49 PM

"Gunshots are characterized by a supersonic muzzle blast, followed by the usually supersonic bullet, ..."

Shouldn't that be PRECEDED by a supersonic bullet? If the bullet is supersonic, then by definition it's traveling faster than the sound of its muzzle blast, right?

^ ^ the muzzle blast is seen at the speed of light (supersonic) which is faster than the bullet, which is also supersonic, but slower than the speed of light. follow?

Corey CopelandJanuary 8, 2015 10:31 PM

I lived in the MPLS Elliot Park neighborhood in 94'/95' and it was a problem (gun shots.) The bible college I went to briefly was a big help in combating crime. (The whole good vs. Evil) There was an improvement (less) shootings..anyway it would be great to see a technology preventing crime ..just no "Minority Report" (great movie though.) Changing Opinion..Paul Simon lyrics came to mind for some reason regarding this topic.

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