Things You Should Know But Don’t: Gunshot Detectors

Posted August 28, 2023

In the late 80s and early 90s, the US saw a spike in gun-related deaths—historically, until 2021, this had been the largest spike in the nation’s history. It was also the era when the US saw the first implementation of gunshot detection technology (GDT) in Redwood City, CA. In 1996, the LA Times reported that, “last month, officials here conducted the first tests of a system that uses acoustic sensors—fancy microphones—to detect gunfire in the streets.” The same article mentioned that other cities at the time had a growing interest in the technology.

By 1998, the National Institute of Justice (NIJ) began researching the effectiveness of GDT. It concluded that these systems can be effective in increasing police response time as well as improving police data. When gunfire data is included in police databases and examined alongside other information about local criminal hotspots, crime forecasting can improve along with efforts to work towards long-term solutions. As of 2016, most major metropolitan cities in the US now use some sort of GDT in their policing efforts.

While these “fancy microphones” have come a long way since 1996, GDT still uses acoustics to determine if there has been a gunshot in a certain area. There are typically two or more sensors placed in a location that need to positively identify a sound as a gunshot before local police are alerted. Acoustic sensors can also triangulate the source of the gunfire and its trajectory, which can give emergency responders important information about the situation they’re entering. Most famously, GDT and its triangulation capabilities were used to collect data on the Ohio highway sniper in 2003 and helped in the capture and arrest of the shooter.

In addition to acoustic detection, GDT uses pressure sensors that can detect the change in air compression that happens when a bullet is discharged. In more recent years, many GDTs have started to use infrared sensors as well. When a firearm is shot, it creates an optical flash that lets off visible and infrared light. When GDTs can detect both acoustic information and infrared, the number of false positives decreases. When the NIJ initially reported on the acoustic systems implemented in Redwood City by Shot Spotter—a well-known company that manufactures gunfire detection systems— they had an accuracy of 80%. This was increased to 97.69% in a study conducted from 2019-2021 by the same company. Shot Spotter has also started introducing AI into their analysis process.

Finally, one of the newest developments in GDT has been the introduction of portable systems. Historically, when a city installed GDT, the sensors were placed in permanent and fixed locations. Since 2000, the number of mass shootings in the US have been drastically increasing in terms of both incidents and victims. Shooters often target events or places with high concentrations of people—in fact, the deadliest mass shooting in the US was at a concert in Las Vegas, NV in 2017. Having a GDT with portable capabilities for events taking place in an area lacking a permanent system can help improve police response time, which is crucial in the event of an active shooter.

For all its positive use cases and technological advancements, GDT is not without its flaws. It has been criticized for increasing stop and frisk tactics, skewing data based on sensor placement, and escalating violence in the event of a false positive alert. GDT is also limited to being reactionary, rather than preventative.  Some argue that money spent on implementing these alert systems would be better spent towards improving gun control laws and community improvement projects.

If you’re interested in this and other tech used by law enforcement like the FBI, be sure to check out my previous blog entries on this topic.

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