Field Evaluation of the ShotSpotter Gunshot Location System: Final Report on the Redwood City Field Trial

The ShotSpotter gunshot location system is comprised of three primary components: (1) acoustic sensor modules located in the target area; (2) base station (personal computer) located in the police dispatch center; and (3) software that monitors all channels for gunshot sounds and then computes relative time delays between detections on different acoustic sensor modules. About eight acoustic sensor modules are required to cover a square mile area. The ShotSpotter system costs $150,000 for the first square mile and an additional $100,000 to $120,000 for each additional square mile of coverage. The ShotSpotter system was tested in Redwood Village in Redwood City, California, a neighborhood of about one square mile and known for a high incidence of celebratory and random gunfire. Testing involved the installation of eight acoustic sensor modules on various rooftops of residences and buildings in the experimental target area. These modules were disguised by their design, and some resembled heating vents while others resembled bird houses. In tests conducted in June 1997, 32 locations were randomly selected from where blank rounds would be discharged. Three types of weapons and the number of rounds to be fired from each weapon were randomly assigned to each of the selected locations. The ShotSpotter system was able to detect nearly 80 percent of test shots. Specifically, the technology annunciated shotgun rounds at the highest rate (90 percent), followed by pistol rounds (77 percent) and assault rifle rounds (63 percent). The technology was able to locate 84 percent of test shots within a median margin of error of 25 feet. Proponents of the technology said the technology was advantageous because it could pinpoint gunfire incidents more quickly and accurately. Opponents of the technology indicated that it had no impact on the arrest rate of persons discharging weapons. Police officers did not have as much confidence in the ShotSpotter system's ability to identify or locate random gunfire incidents. More specifically, police officers did not believe the technology improved their response times to random gunfire calls for service over and above citizen-initiated events. Additional information on system evaluation procedures and protocols is appended. 3 references, 14 tables, and 1 figure