Acoustic gunshot detection systems, which have been adopted by more than 90 US jurisdictions,1Jillian B. Carr and Jennifer L. Doleac, “The Geography, Incidence, and Underreporting of Gun Violence: New Evidence Using ShotSpotter Data,” The Brookings Institution, April 2016, 4-5, https://brook.gs/2J7zgej. have the goal of accurately detecting and locating gunfire in order to improve police response to gunshot incidents.2Kyung-Shick Choi, Mitch Librett, and Taylor J. Collins, “An Empirical Evaluation: Gunshot Detection System and its Effectiveness on Police Practices,” Police Practice and Research 15, no.1 (2014): 48-61; Dennis Mares and Emily A. Blackburn, “Evaluating the Effectiveness of an Acoustic Gunshot Location System in St. Louis, MO,” Policing 6, no. 1 (January 27, 2012): 26-42. With this technology, sensors that can detect acoustic soundwaves produced by gunfire are placed strategically throughout a targeted area.3Michael Litch and George A. Orrison, IV, “Draft Technical Report for SECURES Demonstration in Hampton and Newport News, Virginia,” (unpublished report, January 2011): 31-34, https://www.ncjrs.gov/pdffiles1/nij/ grants/233342.pdf; Mares and Blackburn, “Evaluating the Effectiveness;” Choi, Librett, and Collins, “An Empirical Evaluation.” When a gunfire-like sound is identified, the location is triangulated, and within a minute, an alert is sent to local police that includes the location (latitude and longitude) of the incident, the time, and an audio recording.4Litch and Orrison, “Draft Technical Report;” Mares and Blackburn, “Evaluating the Effectiveness;” Choi, Librett, and Collins, “An Empirical Evaluation.” The software provides police with accurate location information; as a result, gunshot detection systems can help police more quickly respond to gunfire as compared to when it is reported through other methods (e.g., a 911 call).5Litch and Orrison, “Draft Technical Report;” Mares and Blackburn, “Evaluating the Effectiveness;” Choi, Librett, and Collins, “An Empirical Evaluation.” Additionally, these systems can alert police to gunshots that might have otherwise gone unreported—though in both of these cases, it also increases the frequency of false positives.6Litch and Orrison, “Draft Technical Report;” Mares and Blackburn, “Evaluating the Effectiveness;” Choi, Librett, and Collins, “An Empirical Evaluation,” 51-52; MacArthur Justice Center, “End Police Surveillance,” accessed November 9, 2022, https://endpolicesurveillance.com/; Jerry H. Ratcliffe et al., “A Partially Randomized Field Experiment on the Effect of an Acoustic Gunshot Detection System on Police Incident Reports,” Journal of Experimental Criminology 15, no. 1 (March 2019): 67–76, https://doi.org/10.1007/s11292-018-9339-1; Nick Selby, David Henderson, and Tara Tayyabkhan, “ShotSpotter Gunshot Location System® Efficacy Study,” CSG Analysis, 2011, https://www.shotspotter.com/wp-content/uploads/2020/12/ShotSpotter_Efficacy_Study_062311_FPV.pdf. Limitations to technology are also described below.
Research has shown that properly implemented gunshot detection systems are very effective at accurately detecting and locating gunfire.7Cory Watkins et al., “Technological Approaches to Controlling Random Gunfire–Results of a Gunshot Detection System Field Test,” Policing 25, no.2 (2002): 345; Carr and Doleac, “Geography, Incidence, and Underreporting of Gun Violence;” Litch and Orrison, “Draft Technical Report.” Studies have also found that the use of a gunshot detection system can improve police response times to gunshot incidents8Choi, Librett and Collins, “An Empirical Evaluation;” Mares and Blackburn, “Evaluating the Effectiveness.” and can help alert police to gunfire that otherwise would have gone unreported.9Litch and Orrison, “Draft Technical Report.” Gunshot detection systems can also provide police with accurate gunshot data that can be analyzed in order to develop innovative solutions in places with repeated gun violence.10Watkins et al., “Technological Approaches;” Andrew Merrill, “The Life of a Gunshot: Space, Sound and the Political Contours of Acoustic Gunshot Detection,” Surveillance and Society 15, no.1 (February 28, 2017): 42-55. However, due in large part to limited data availability, there is not currently evidence to suggest that shootings are prevented or solved at a greater rate, or that injuries or deaths are reduced based on the presence of gunshot detection technology.11Choi, Librett, and Collins, “An Empirical Evaluation, 48–61; Mitchell L. Doucette et al., “Impact of ShotSpotter Technology on Firearm Homicides and Arrests Among Large Metropolitan Counties: A Longitudinal Analysis, 1999–2016,” Journal of Urban Health, April 30, 2021, https://doi.org/10.1007/s11524-021-00515-4; Anna Goldenberg et al., “Use of ShotSpotter Detection Technology Decreases Prehospital Time for Patients Sustaining Gunshot Wounds,” Journal of Trauma and Acute Care Surgery 87 (2019): 1253–59; Mares and Blackburn, “Evaluating the Effectiveness;” Dennis Mares and Emily Blackburn, “Acoustic Gunshot Detection Systems: A Quasi-Experimental Evaluation in St. Louis, MO,” Journal of Experimental Criminology 17, no. 2 (June 2021): 193–215, https://doi.org/10.1007/s11292-019-09405-x. Additionally, gunshot detection softwares have a higher-than-baseline rate of false positives, which increase police workloads and may risk impairing police-community relationships.12MacArthur Justice Center, “End Police Surveillance;” City of Chicago, Office of Inspector General, “OIG Finds that Shotspotter Alerts Rarely Lead to Evidence of a Gun-Related Crime and that Presence of the Technology Changes Police Behavior,” press release, August 24, 2021, https://bit.ly/3G0CHBI; Ratcliffe et al., “A Partially Randomized Field Experiment;” Selby, Henderson, and Tayyabkhan, “ShotSpotter.”
To implement a gunshot detection system, law enforcement agencies contract with a company that provides the necessary equipment and training.13Matt Drange, “We’re Spending Millions on This High-Tech System Designed to Reduce Gun Violence. Is It Making A Difference?” Forbes, November 17, 2016, https://www.forbes.com/sites/mattdrange/2016/11/17/shotspotter-struggles-to-prove-impact-as-silicon-valley-answer-to-gun-violence/#d8a8a3e31cb4. The equipment is typically leased rather than purchased, and the agency then pays an annual subscription fee for its use and maintenance.14Drange, “We’re Spending Millions.” This arrangement can help law enforcement agencies save on upfront costs, but it does allow the provider company to retain ownership of the gunshot data collected.15Drange, “We’re Spending Millions.” The actual annual costs will depend on the coverage area and how many sensors an agency deploys.16Drange, “We’re Spending Millions.”
Strategy in Practice
Gunshot detection systems are also aligned with problem-oriented and predictive policing models, as this technology is typically installed in gun crime hot spots and provides data that can be used to help develop solutions to the problem of gunfire within the community.17Watkins et al., “Technological Approaches;” Mares and Blackburn, “Evaluating the Effectiveness.”
Gunshot detection technology is designed to immediately notify first responders in real-time when sensors detect gunfire. Once the acoustic sensor captures perceived gunfire, your public safety agencies may use either audio playback or integration with nearby crime cameras to verify the gunfire incident. If there is evidence of an injury, notifications should trigger an immediate response from your emergency medical personnel to deliver potentially life-saving care and transport injured people to the nearest hospital.
Your local law enforcement agency then deploys nearby patrol officers to investigate the scene of the potential shooting. Responding officers should note and, where appropriate, collect any evidence of a shooting (e.g., bullets, spent cartridges, or damaged property). The appropriate investigations team then conducts follow-up and takes over the shooting investigation once the initial scene has been processed.
False positives: False positives occur when a gunshot detection system is activated by something other than gunfire (e.g., fireworks).18Litch and Orrison, “Draft Technical Report.” Data limitations make it difficult to determine exactly how common false positives are in gunshot detection technology notifications, but several research reports and peer reviewed journals find that they’re a frequent challenge that increases police workloads and risks unnecessarily sending police into already vulnerable communities expecting to encounter a shooting, and thus increasing the likelihood of police violence.19MacArthur Justice Center, “End Police Surveillance;” City of Chicago, Office of Inspector General, “OIG Finds that Shotspotter Alerts Rarely Lead to Evidence;” Ratcliffe et al., “A Partially Randomized Field Experiment;” Selby, Henderson, and Tayyabkhan, “ShotSpotter.” Some police agencies have attempted to address this problem by having a staff member manually listen to the recording of the incident to confirm whether it captured gunfire or some other noise.
Limited detection abilities: Though studies have found that gunshot detection systems are overall effective at detecting and locating gunfire, it remains difficult for this technology to detect shots fired indoors or by guns equipped with high-quality suppressors.20Mares and Blackburn, “Evaluating the Effectiveness.”
Limited impact on the resolution of gunshot cases: Many evaluations of gunshot detection systems have found that, although the technology can help improve police response times and confer other benefits, the use of these systems rarely leads directly to the arrest or prosecution of a shooter.21Choi, Librett, and Collins, “An Empirical Evaluation;” Mares and Blackburn, “Evaluating the Effectiveness;” Drange, “We’re Spending Millions.” Additionally, research is still unclear as to whether gunshot detection systems can actually reduce or prevent shootings or related injuries or deaths.22Ratcliffe et al., “A Partially Randomized Field Experiment;” Litch and Orrison, “Draft Technical Report;” Drange, “We’re Spending Millions;” Choi, Librett, and Collins, “An Empirical Evaluation;” Mares and Blackburn, “Evaluating the Effectiveness;” Doucette et al., “Impact of ShotSpotter Technology;” Goldenberg et al., “Use of ShotSpotter Detection;” Mares and Blackburn, “Evaluating the Effectiveness;” Mares and Blackburn, “Acoustic Gunshot Detection Systems.”
Agencies, Organizations, and Other Necessary Partners
Gunshot detection system provider: Law enforcement agencies will need to contract with a company to receive the equipment and training to implement a gunshot detection system.
Community partners: Community involvement in the deployment of a gunshot detection system and access to the data could help increase the technology’s deterrent effect and help strengthen police-community relationships.23Watkins et al., “Technological Approaches.” When shared with community members, this data can be vital in helping to identify key drivers of gun violence, which can be collaboratively addressed to help reduce it. Community-led violence intervention programs can also serve as co-responders to the scene, and play a vital role in developing and implementing data-informed strategies for addressing shootings in their communities.
What Else You Need to Know
Gunshot detection systems can be paired with other technologies and community engagement to enhance surveillance capabilities and generate more actionable evidence.24Ratcliffe et al., “A Partially Randomized Field Experiment;” Choi, Librett, and Collins, “An Empirical Evaluation.” For example, some places electronically tie gunshot detection systems to closed-circuit television (CCTV) cameras so that once a gunshot is detected by the audio sensor, the camera is triggered and pans toward the direction from which the shot originated.25Ratcliffe et al., “A Partially Randomized Field Experiment;” Choi, Librett, and Collins, “An Empirical Evaluation.” This can help officers and dispatchers see the location of the gunfire and reduce reliance on eyewitness testimony, though this technology too suffers from limitations related to monitoring, placement, and interpretation biases.26Choi, Librett, and Collins, “An Empirical Evaluation.” Gunshot detection systems can also be synced to screens located inside police cruisers27Choi, Librett, and Collins, “An Empirical Evaluation,” 58-59. and to mobile apps,28David Welsh and Nirmalya Roy, “Smartphone-Based Mobile Gunshot Detection,” Institute of Electrical and Electronics Engineers, 13th Workshop on Context and Activity Modeling and Recognition (2017), https://userpages.umbc.edu/~nroy/courses/shhasp18/papers/p244-welsh.pdf. which makes the technology more flexible and user-friendly for officers. Data transparency and a further-developed evidence-base can also be achieved by making gunshot detection software publicly available.