Program Goals/Target Sites
Gunshot detection systems are used by law enforcement to detect, respond to, and investigate gunfire. They are usually installed in high-crime urban areas as part of targeted interventions to reduce firearm-related crimes and violence in specific neighborhoods. The system improves police response to gunshots in two ways: 1) it alerts police to gunshots when there is no other notification (such as citizen calls for service or patrol officer observation), and 2) it shortens response time when there is notification, especially through a 911 call or other citizen call for service. Gunshot detection systems are completely automated and designed to notify police every time a possible gunshot is detected. In addition, the location information the system provides is much more accurate (within a few meters) about where the sound occurred. Citizen reports are not as accurate, which can increase police investigation time.
Gunshot detection technology was originally developed by the military to detect the location of enemy snipers on the battlefield, but it was adapted for civilian purposes and has become increasingly popular for law enforcement purposes over the past 15 years. Typically, an area of 1 to 3 square miles of a high-crime urban area is selected for installation, and an array of sensors is mounted to rooftops, telephone poles, and other elevated structures throughout the area. The technology is designed to detect outdoor gunshots in a specific area of coverage, and is not typically activated by indoor gunshots.
The systems comprise a series of acoustic and/or optical sensors installed across high-crime areas that are calibrated to detect high-decibel impulsive sounds, such as gunshots. When a sensor is triggered, this data is sent to a central processing unit, which collates the data from all of the sensors triggered in the area. Using GPS technology, the unit can triangulate the location of the gunfire and thus provide precise latitude and longitude coordinates as well as street addresses. Information on the gunfire’s location and type of gun fired is then sent to the police department—this information can arrive as quickly as 20 seconds after the gunfire is detected. Once the information is received by the police station, officers are dispatched to the scene. Some systems have the capacity to interface with cameras, which refocus in the direction of the shot(s) fired to provide visual data.
The study by Scharf, Geerken, and Bradley (2008) showed promising results with regard to the gunshot detection system’s (SECURES) ability to improve gunshot detection within a community, as well as for improving data accuracy for gunshot events. However, results did not show a significant impact on the technology’s ability to reduce crime.
Detection of Live Fire
The system was very accurate in its ability to detect gunshots (97 percent detected), except for .22 caliber firearms (33 percent detected). The system activated for 50 percent of bottle rocket discharges (although more often they activated as an aerial rather than a ground event) and for 35 percent of the firecrackers (as ground events).
Identification of Gunshot Location
The system very accurately located gunshots—in most cases within a 10-foot radius of the precise location where the shot was fired.
Detection of Gunshot Events
The system detected more events than calls for service. In Hampton, 18 percent of SECURES-related dispatches had associated 911 calls. This means that SECURES alerts accounted for 82 percent of dispatches, with no associated call for service. It does not mean, however, that all SECURES alerts were gunshot incidents; there may have been cases of false positives in which an alert was sent for a noise that was not a gunshot.
Crime and Clearance Rates
Results showed no pattern of a deterrent effect for offenses reported to police. In fact, violent offenses, weapons offenses, and other offenses actually increased in areas that implemented the SECURES system from the pre- to post-implementation period. For example, violent offenses increased 8 percent from the pre- to post-implementation period in SECURES areas, while non-SECURES areas saw a 10 percent increase.
The data provided sparse evidence for an impact on clearance rates for violent and weapons crimes. In Hampton, weapons-related dispatches generally accounted for a lower percentage of all dispatches. However, the number and percentage of weapons-related dispatches more than doubled in areas covered by the SECURES system.
The system more than doubled the number and percentage of weapons-related dispatches in the coverage area. Of the 84 total alerts that initiated dispatches, only 23 (27.4 percent) were confirmed as actual gunshot events by witnesses or physical evidence.