a compilation of the Surveillance technology Impact Reports referred by the City Council to the Public Safety Committee

SURVEILLANCE TECHNOLOGY IMPACT REPORT (Revising STIR No. 24 Submitted December 9, 2019; Supplemented January 22, 2020) Department: Police Division or Unit (if applicable): CID Days; DV/SA; Cyber Submitted by: Jim MulcahyCommissioner Branville Bard Date: 12/9/192/24/2020 Surveillance Technology: Shotspotter 1. Describe how the proposed Surveillance Technology will work, including how it will collect Surveillance Data. x Gun shot detection system x Shotspotter is a gun shot detection system. Gun shot detection systems are designed to be an ever-vigilant reporting ear. In many neighborhoods across the country, residents have become so immune to the sound of gunshots that many incidents go unreported—many criminals count on this indifference and become emboldened in such environments. Gunshot detection systems provide a perpetual reporting ear and alert law enforcement of these incidents. x Here is a diagram of how the location of gunfire is obtained using an acoustic triangulation system [this is meant to serve as an overview, not to provide highly detailed knowledge]: o Because the speed of sound in air is a known entity—340.29 meters per second [.21 miles per second] at sea level—the difference in the time it takes for the sound/shockwave of a gunshot to reach three different sensors can determine the location of that gunshot. Using a built-in GPS system as an accurate time source, three sensors work together to triangulate the location from which a shot was fired (illustration below). Example: o A shot is fired somewhere in the city. Sensor 1 picks up the sound of the shot. Since each acoustic sensor has a range of about 2 miles, we know that the shot was fired within a 2-mile radius of Sensor 1. 51

o One second later, Sensor 2 picks up the sound waves of a gunshot. Based on the known speed of sound, we know that the shot was fired approximately one-fifth of a mile farther away from Sensor 2 than Sensor 1. We can draw a circle representing the perception radius of Sensor 2 overlapping the perception radius of Sensor1—since both sensors picked up the sound waves, the shot must have been fired within the overlapping coverage areas. Where the two circles intersect, we have two possible locations for our gunshot. o To figure out which of these two points is the location from which the shot was fired, we need to find a third sensor that picked up the sound of the shot. A third sensor, located to the south of Sensors 1 and 2, picked up the sound waves a half-second after Sensor 2 detected them. This would put the origin of the sound about one-tenth of a mile farther from Sensor 3 than from Sensor 2. o We now have our gunshot location [indicated in the above illustration as the point where all three circles intersect] at least in terms of distance from the sensors. The systems then use built-in GPS receivers to convert that known point into latitude and longitude coordinates, where it is converted into a 52

numerical address. This complex process takes seconds and arms law enforcement with the “exact” location.7 x CPD has no listening capabilities; sensors are analyzed at Shotspotter HQ in California. Only incidents identified by Shotspotter’s proprietary algorithm as “in the class of gunshots” generate a numerical address sent to the Department via the application. No other audio is sent to or sought by CPD. 2. What is the purpose of the Surveillance Technology? x Identifying and preventing threats to persons and property and preventing injury to persons or significant damage to property x Identifying, apprehending, and prosecuting criminal offenders x Gathering evidence of violations of any law in criminal, civil, and administrative actions 3. Where will the Surveillance Technology be deployed? When? x Deployed across the City with 12 sensors and a 1.1 square mile coverage area 4. What privacy impact will the Surveillance Technology have? x This technology has minimal impact as it captures the sound of gunshots. CPD has no listening capabilities; sensors are analyzed at Shotspotter HQ in CA, only. Only incidents identified by Shotspotter’s proprietary algorithm as “in the class of gunshots” aregenerate a numerical address sent to the Department via the application. No other audio is sent to or sought by CPD. The placement of microphones has not changed since the implementation of the technology; initial placement was based on prevelanceprevalence of gunfire or gunshot victims. CPD has the ability tocan request movement but the high concentration (relative to Cambridge) has persisted in the same area. 5. What are the fiscal costs of the Surveillance Technology, including initial costs, ongoing maintenance and personnel costs, and source of funds? x The technology has a cost of approx. $50K /yr., which is funded by the Urban Area Security Initiative (UASI); the City would be responsible for continuing cost should the funding cease. 7 http://science.howstuffworks.com/shotspotter.htm 53