Hacker News Reader

Comment by zheng | Hacker News Reader

I'm not 100% on the laws around this, but if a city was utilizing ShotSpotter, wouldn't they have to disclose the area(s) they were monitoring?

View on HN

My city (Springfield MA) has a shotspotter system, and even though I have pretty high-up contacts among Springfield PD who know that my interest in the system is purely academic (I'm an acoustical consultant) they wouldn't reveal to me any of the transducer locations. In fact just trying to find a picture of a shotspotter transducer is difficult (the pic in the NYT link is only the second one I've seen).

The sensors are very easy to spot. They are small, white/pale-grey boxes about 4 inches square by 2 inches deep. They're usually placed on stop light struts or on free-standing poles by themselves. They're easy to mistake for emergency vehicle "light changer" systems, but the difference is these are on roads where there are no stop lights. Also, I've seen clusters of 3 or 4 of them attached to the same pole that a camera is attached to -- presumably the camera automatically pans and zooms in on the area as soon as a shot is heard.

They are small, white/pale-grey boxes about 4 inches square by 2 inches deep.

Are you sure about that? That doesn't jibe with the picture I've seen (http://i.imgur.com/XBevy.jpg) and doesn't sound optimal for an acoustic transducer.

I'm 99.9% sure that is NOT a shot spotter. We have Shotspotter in some areas Minneapolis, as well as city-wide wifi. Those little cans are all over the place and are part of the WiFi System. I took a photo of one just down the street from my house: http://i.imgur.com/OqYEA.jpg

The can looks like a BelAir Networks BelAir200 WiFi Node.

As another poster mentioned, that's most likely a wifi access point.

I spent the last few minutes poking around StreetView looking for a photo of the units I'm thinking of without luck (the dates Google lists on their StreetView seem quite incorrect), but a hard, flat surface would be perfect for a sound transducer. It'd also be easier to weatherproof than something with microphones dangling outside.

I spent the last few minutes poking around StreetView looking for a photo of the units I'm thinking of without luck

In my city I know that they periodically move the units so it may be that they were moved when the pics were taken.

but a hard, flat surface would be perfect for a sound transducer.

I would be surprised if the mic was embedded in a flat surface, that would cause all sorts of diffraction problems for a surface that wasn't (effectively) infinite, especially since there is a lot of high-frequency energy in gunshots. I suppose they could try to equalize them out, but that seems like unnecessary work. But again, I haven't seen a (confirmed) transducer.

It'd also be easier to weatherproof than something with microphones dangling outside.

edit: actually I suppose the mic could be offset just an inch or so from the enclosure, that would be enough to reduce diffraction problems while not being noticeable from a distance. I'd love to see one of these systems up close. That problem has long since been solved with metal diaphragm mics, especially at the price points they're targeting. Microphones in airport monitoring systems last for years.

edit 2: some more searching indicates that a unit is actually made up of an array of mics. In that case, a flat surface would make perfect sense.

my understanding is that anyone can record any visual or auditory info from any public place (in the US)

Unless you use a telephone to do it or are using a telephone when you're being recorded?

I understand that making a recording of a phone call without notification is strictly disallowed in many states legislation? (eg http://en.wikipedia.org/wiki/Telephone_recording_laws#United...)

Telephone systems are a public place?

If I'm walking down the sidewalk talking on my phone, overhearing my voice is not a violation of privacy.

>overhearing my voice is not a violation of privacy //

But we're talking about recording your voice. Which I think is a violation of my privacy vs just listening to me passively - now that may not be enshrined in any law but then the law doesn't IMO [exclusively?] dictate what is moral.

Think point is. Unless that voice is carried over telecommunications network to, say central processing center.

Reply on news.ycombinator.com