Find the gunshots, but preserve privacy
August 02, 2015
ShotSpotter can only be triggered by gunshot-like noise
Most people don’t immediately recognize the sound of gunfire. In many lucky places, that cracking pop is as likely to be a backfiring car or a firecracker as a bullet whizzing lethally through the air.
But not all places are lucky. In some neighborhoods, gunshots are as common as the tweeting of birds – or the wailing of sirens – and the frightened residents who call 911 know that whoever fired that weapon will be long gone by the time police arrive.
So it’s good news that Sacramento has found room in its budget for a yearlong pilot project aimed at improving the emergency response to gunshots. At a news conference last week, Sacramento Police Chief Sam Somers Jr. said the city has been experimenting since June with an increasingly popular gunfire detection technology.
The system, devised by the Bay Area-based firm SST Inc. and known as ShotSpotter, can pinpoint the sound of a gunshot within seconds after it occurs, allowing police to get to the scene in less time than it would take a caller to report it.
In use in about 90 cities, including Oakland, New York, Denver, Boston and Fresno, it relies on a network of acoustic sensors that are placed high on utility poles, buildings and other structures. The sensors record constantly on a spool, listening for a specific range of high-pitched and explosive noises.
ShotSpotter’s web site says the network can’t overhear conversations. Still, 20 microphones per square mile raise privacy questions.
When the right sound is detected, the sensor alerts a centralized server, and when three or more sensors in an area are triggered, the server downloads the snippet of audio and transmits it to the company’s monitoring station near Fremont. There – all this happens in a matter of seconds – humans quickly review it and forward the tape and triangulated location to authorities.
Somers calls the technology “game-changing,” and it would be in some parts of the city. In the first four months of this year in North Sacramento, police dispatchers logged an average of nearly three reports of “shots fired” each day.
In the pilot area alone, police say, the sensors already have detected scores of gunshots and helped lead to at least three arrests and the confiscation of at least four guns.
But there is a price to this experiment – two prices, really. First, the sensors are expensive; the Police Department is paying $180,000 just to create and monitor a 3-square-mile pilot network.
And second, there are microphones and recorders in those sensors. ShotSpotter’s website says the network can’t overhear normal speech or street conversations, is “intentionally designed not to permit any ‘live listening’ of any sort” and can only be triggered by gunshot-like noises.
Still, 20 microphones per square mile – even if they’re on utility poles and rooftops – is a recipe for privacy issues, if not now, then in the future. Though the company says its networks have detected millions of gunshots, in at least two cases, human shouts or screams showed up on a downloaded snippet.
Sacramento should be deliberate in measuring the pros and cons of this pilot, and as transparent as possible in its assessment. From GPS trackers to license plate scanners to body cameras, technology is revolutionizing public safety, but crime-stopping must be balanced with civil liberties.
Note from ShotSpotter: