
Shotspotter CEO Answers Questions on Gunshot Detectors in Cities - CapitalistCartr
https://www.aclu.org/blog/free-future/shotspotter-ceo-answers-questions-gunshot-detectors-cities
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admax88q
The privacy concerns with systems like these is not what they currently do,
but what they are capable of.

It doesn't matter what your privacy policy says, and it doesn't matter if the
default configuration is to only download the audio near the time of a
possible gunshot.

The important part is that these devices can stream audio to remote servers.
The NSA or anybody who finds or can coerce accesses to the system could use
them to eavesdrop on everything within range.

No amount of "privacy policy" is going to prevent it.

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wl
That's assuming that audio from these sensors is at all useful for
eavesdropping on people. Try a speakerphone lately? Even with higher quality
codecs than we got in the POTS days and things like beamforming, the result is
pretty terrible in decent sized conference rooms. Now try this outdoors,
further away from people, with the noise floor of a city instead of a quiet
room.

The cases people point to where ShotSpotter has picked up understandable words
have been people very close to sensors who were shouting immediately before,
during, or after gunfire the system picked up. But at that point, it's
unreasonable to claim some sort of violation of privacy when people are
screaming for all to hear.

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Animats
Redwood City, CA had the first system. It was much simpler than this. They had
analog microphones on phone poles, connected to a logarithmic amplifier which
traded dynamic range for bandwidth. Phone audio is 8 bits at 8KHz; think of
this as remapping to 16 bits at 4Khz, although it was done with analog
hardware. They needed the dynamic range to see the full risetime of a gunshot,
and gave up a big chunk of the voice spectrum to get it.

Each microphone had a wired phone line connection to the central system at the
police station, which was a PC with a data collection card running LabView. A
LabView program turned gunshot information into map plots. It was a simple,
local system.

The new systems are much fancier. They're "cloud-based", which means the data
goes first to ShotSpotter's HQ. They have synchronized clocks (probably from
GPS), so they can send in timed audio snippets to be matched at the analysis
center. It's a service now, rather than just hardware. Not clear what kind of
data connection they have; probably cellular data.

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jagermo
Wait - what? There are so many guns fired in US cities that a company can
build a sustainable business creating a system that spots these gunshots?

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dntrkv
I've lived in Sacramento, Portland, and now San Francisco and I have yet to
hear a gunshot in any of these cities.

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jagermo
Right? I thought that was just something from TV/Movies - this looks more like
they are selling fear than something real.

Why would a city invest in something like this? Especially if you get the
information via emergency calls?

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saynay
I happened to start working with a similar system today. For our customer
there are several factors they are interested in:

# Mapping gunshots in both time and space. These types of sensors can attempt
to classify the type of weapon used based on the audio signature. If there are
are several shots from similar-sounding sources moving through the city at a
certain, or in a certain area over the period of days (or month), this can
tell you more than you could determine from just emergency calls.

# Tieing the gunshot sensors in with other input devices, like cameras. You
can reduce the time spent looking through, say, traffic camera recordings that
happened in the vicinity of the gunshot looking for related video.

# Automatically pointing moveable cameras to look in the direction of a
gunshot. Means you don't need as many camera for the same effective coverage.

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TruthSHIFT
Does this technology have a slippery slope? Assuming that the technology isn't
useful for recording conversations, what's the worst that could happen by
implementing this in residential neighborhoods?

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jagermo
As far as I see it you waste money that could be better used in staffing
police, implementing social programs etc - this thing is a solution to a very
tiny problem: gunshots that are not reported via emergency calls. As far as I
can see this does not help with robberies, burglaries, attacks with
fists/knives/bats etc.

Even if its not a slippery slope - I'd imagine there are several better
alternatives where you can spend the money.

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detaro
> this thing is a solution to a very tiny problem: gunshots that are not
> reported via emergency calls

I wondered how big a problem this is, but the only number I quickly could find
is annoyingly from their advertising material and claims that in some areas
only 10 % of shots were reported, which is not really the relevant number.
Does anyone have a number on how many people die of gunshot injuries that
either weren't reported or reported to late?

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CHY872
That's also not the relevant number. In places like Chicago, what you end up
with is a tiny proportion of the population (say 2000) that is perhaps 100
times more likely to be murdered and is a major drain on your city's image.
This is fuelled by revenge killings; someone gets shot or shot at, their
family/friends round up the posse.

So what you want to do is get people off the street before they start
shooting, or if that fails, you get them off the street as soon as they start
shooting in order to break the cycle.

At the moment, with the dispatching of officers etc, you find that it takes
about 2 minutes from receiving a call to an officer being dispatched (that's
from the London Ambulance Service). A lot of this is just the time between the
call arriving and the operator working out where the person is. Before the
call, there are perhaps 15 seconds where the bystander who calls up is getting
their phone out and dialing.

In this case, with the new system you can in principle have two squad cars
each half a mile away knowing where the gunshot is to a reasonable level of
accuracy, perhaps within a couple of seconds of the shot itself.

Within a minute of the first shot, the police can be on the scene. In this
case, the suspects have only just jumped into their cars, and so are picked up
easily.

There's no opportunity for any kind of revenge, because the suspects are in a
cell.

Of course it's not a fantastic idea for every city; but if you're a company
that focuses on military hardware, filtering off into LA, Chicago and NY can
easily be an advantage for all.

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jbob2000
But why? Why do you want to know when a gunshot happens? By the time you've
heard it, it's already too late.

“You were so focused on whether you could do it, you never stopped to ask
whether you should.” - Jurassic Park

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NoMoreNicksLeft
Is it possible to create a (cheap) non-firearm device that mimics gunshots
closely enough to fool the system?

Would be fun to put dozens up all around, on slow timers.

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hga
Depends on the sophistication of the system, and how many microphones it has.
The vast majority, if not pretty much all of this class of gunshots, are going
to start with the bullet being supersonic, the shock wave of which contributes
to the signature (in the case of sniper fire I mentioned elsewhere in this
discussion, it will tend to fool people into thinking the source is as much as
90 degrees from where the rifle actually is).

I'm having difficultly coming up with anything that isn't essentially a blank
firing gun, and I'll note those are deadly really close up.

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NoMoreNicksLeft
So, a firecracker won't do the trick? I realize that's still explosive, but
unless you're stuffing them up a nostril first they're pretty safe.

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hga
To my thoroughly trained ears they sound very different.

Thinking about it, to avoid false positives, companies doing this need to
filter out fireworks, the proverbial car backfire (do they do that any
more???), etc.

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aorloff
I'm not an expert, or even a layman in audio encoding, but it seems to me that
a solution could be found that couples an open source capture program with
their backend. The open source (audited and only updated from the open source
branch) capture program filters the audio stream down to something that only
contains a gunshot signature, and nothing else. If the motivation is there a
solution is certainly possible.

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toomuchtodo
It could be done, similar to this lightning detection project:

[http://www.lightningmaps.org/realtime](http://www.lightningmaps.org/realtime)

[http://www.blitzortung.org/Webpages/index.php?lang=en&page=3](http://www.blitzortung.org/Webpages/index.php?lang=en&page=3)

TL;DR They do triangulated time of flight for EM emissions from lightning
strikes.

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CHY872
Thing is, with lightning it is _dead_ easy because you're talking about what
is essentially a straight line through the atmosphere.

In a city, you get more issues: double datapoints from the gun and the bullet,
multipath effects, etc etc etc.

