Gunshot Sensors in D.C.

[AJ Dual]

right...I'll bet the waveform of a .380, like someone suggested, never gets altered as it bounces around off of the sides of buildings and the occasional tree.

You're right, it does, but the systems are that good. Honestly, this technology isn't that amazing.

If you think about how digital signal processors, a very "mature" technology since the late 70's early 80's started with things like digital phone calls and CD music, then extrapolate advances that kept pace with the rest of the microprocessor field, the state-of-the-art capability to record and analyize audio information is very advanced.

When you think about how computers and software are capable of things like transcribing human speech with 95% accuracy or better that's commercialy availible for a few dollars, or other tasks like robust facial recognition systems that can function from various angles, and even not be fooled by things like glasses and beards, analyizing audio information for gunshots, and ignoring false positives like firecrackers and backfire is almost trivial.

Determining actual caliber and some general information about the firearm such as barrel length isn't out of the question either.

Since things like buildings and trees don't move very often, echoes will be consistent and may even enhance accuracy. Besides trigangulating the arrival of sound between three or more microphones, echoes can actualy help, since the number of combinations echoes can take between buildings before reaching the microphone is almost infinite, but when you know where the surfaces.that can provide the echoes are, it can be like a fingerprint.

I don't doubt the efficacy of such audio systems at all. I just doubt the efficacy of the police, and ultimately, the politicians they answer to.

 

[Henry Bowman]

As someone who is solidly pro gun, pro freedom, and anti statist, I still don't see why these things aren't a good idea.... in the right place.

I fear that the investments in these systems will be used as an excuse (whether valid or not) against moving suppressors to Title I.

 

[.38 Special]

It also bothers me to see on all the gun boards I'm on, what seems to be knee-jerk reactions to things. I'd like to believe that my fellow gunnies do more thinking than that, and not resort to knee-jerk postings and beliefs that we so often ascribe to DU types.

Amen, brother. You beat me to it. I swear, if the internet had been around when the 911 concept was implemented, there would surely have been a bunch of gunnies yelling about "sheeple" on it.

 

[Threecard]

Fireworks and firecrackers are illegal in DC too. So neither they nor the guns are there.

Walking in downtown DC a few nights ago, I couldn't help but think "If there is one place I need to have a gun...this is it."

That's not saying I was unarmed, however.

 

[xd9fan]

Our nation's capital is a disgrace.

it sure is untrusting and paranoid...of "we the people"
just one more "cool" system that the Govt doesnt need and will be used against us......for our security.

 

[mons meg]

I don't doubt the efficacy of such audio systems at all. I just doubt the efficacy of the police, and ultimately, the politicians they answer to.

Not to discount what you're saying, but I don't doubt the ability of the company that made this system to over-hype it's capabilities. I also don't doubt the ability of people to "game" any system.

For instance, I could start a website, say a free digital "library of sounds". I'll use your high quality audio equipment to record all kinds of different gunshots, maybe offer them up as a downloadable CD. Next thing you know, there'll be a law against "simulating weapon sounds with intent to deceive audio surveillance"

 

[WayneConrad]

Most of what we know about these systems is from those selling it, and from the newspapers printing canned press releases. I think that's responsible for the scepticism exhibited here.

I had to wade through pages and pages of publicity before finding anything resembling a study about any gunshot detection system: Random Gunfire Problems and Gunshot Detection Systems.

Key findings: The study of the use of gunshot detection technology in local law enforcement led the research team to four broad conclusions:

--Gunshot detection systems are likely to reveal rather high citizen
under-reporting rates of random gunfire problems (23 percent of incidents are reported).

--The technology is likely to increase the workloads of police officers, particularly if departments dispatch a patrol unit to every gunfire incident detected by a technological system.

--Gunshot detection systems are not likely to lead to more arrests of people firing weapons in urban settings because it is highly unlikely that offenders will stay at a gunshot location long enough for the police to arrive.

--Finally, gunshot detection systems seem to offer the most potential as a problem-solving tool and would fit nicely within the emerging problem-oriented policing paradigm. The technology can help police identify random gunfire hot spots and develop strategies to address the problem.

Re accuracy of detection:

Of the 31 field trial events, 8 tested the MP5 assault rifle, 13 tested the .38 caliber pistol rounds, and 10 tested the 12 gauge shotgun. The technology annunciated shotgun tests at the highest rate (90 percent), followed by pistol tests (77 percent), and the MP5 assault rifle (63 percent). Overall, the ShotSpotter technology annunciated nearly 80 percent of the test shots (true positives) and failed to annunciate random gunfire events about 20 percent of the time (false negatives).

Re accuracy of location:

The ShotSpotter system identified and triangulated random gunfire events within about 25 feet of the true shot location. Shotgun events had the lowest median location error of 23.5 feet; pistol events were correctly identified within 25 feet of the true shot location; and the MP5 assault rifle tests were identified within 27 feet of the correct firing location.

 

[WayneConrad]

More study results

From Field Evaluation of the ShotSpotter Gunshot Location System: Final Report on the Redwood City Field Trial.

Emphasis mine.

Re cost:

Trilon Technology suggests that approximately 8 acoustic sensor modules are required to cover a one square mile area. Trilon estimates that to purchase the ShotSpotter system will cost approximately $150,000 for the first square mile and an additional $100,000 to $120,000 for each additional square mile of coversage.

Re: why its proponents want it

Proponents of the gunshot location technology felt that the technology was advantageous because it can pinpoin gunfire incidents more quickly and more accurately, people tend to feel safer since its implementation, and installation of the ShotSpotter system has assisted in police community relations.

Re: Cooking the results

The Redwood City Police Department allowed the Evaluation Team to conduct the field test during two time periods: 10:00 am to 3:00 pm and 7:00 pm to 10:00 pm. These times were set by the Police Department in conjunction with Trilon Technology because they avoided heavy traffic hours (rush hour in the morning and rush hour in the evening) and they would not interfere with the majority of residents' sleeping patterns. Avoiding heavy traffic hours decreased the possibility of false positive alerts during our field trial as reduced levels of background noises were somewhat artificially restricted (i.e. car backfires and car horns) through this process. We acknowledge that, in real life situations, such background noises cannot be ignored. However, given the fact that blanks were used as opposed to live round (blank rounds result in the ShotSpotter system registering of wave forms characterized by lower amplitudes) and that the evaulation team wanted to provide the best possible atmosphere for system validation, it was determined that these hours were the best for our field trial.

 

[WayneConrad]

Studies, studies, studies

I forgot to give y'all the link where I found all this stuff: Search results for: ShotSpotter at ncjrs.gov.

 

[ZeSpectre]

Somehow I feel this dovetails right into a previous thread "Affluent friends question desire for CCW in DC"

I'm sure my friends would look at these sensors and say "See, they keep making us safer all the time here in DC".

 

[Manedwolf]

In every test I've read of these systems, even the makers admit that they detect the SUPERSONIC crack of the bullet.

Hence, they'd not detect a .45 or 9mm subsonic.

Hence...utterly useless waste of money. Period.

 

[mdao]

In every test I've read of these systems, even the makers admit that they detect the SUPERSONIC crack of the bullet.

Hence, they'd not detect a .45 or 9mm subsonic.

Hence...utterly useless waste of money. Period.

The field tests were done with blanks... No supersonic cracks there either. Likely, it's keying off of the characteristic sound impulse generated by the firing of a gun. No surprise that the system works better with live rounds than blanks.

By their tests, the systems works reasonably well, and the technology is simple and reasonably robust. Given 3 mikes with enough dynamic range, a copy of LabView, and a bit of additional hardware, I could make a workable facsimile of it by myself.

It's still a bad idea. Overall efficacy of the system in preventing crime is unproven, and they're likely spending hundreds of thousands for a small increase in crime fighting ability. The police don't even have enough resources to be effective now, running after every gunshot event would dilute their strength even more. Criminals are good at adapting, death or jail time is a good incentive, and could quickly neutralize the system. Random shots fired into the air would be work great for distracting cops. I'd also bet the detect rates for .22 LR, .25 ACP, and .32 ACP are quite a bit worse than the rates for 9 mm.

 

[Prince Yamato]

"I'm singing in the rain, just singing in the rain" tappatyy tappatty tappatty.

"Unit 831, reports of machinegun fire on 1st and Pennsylvania."