Fireworks won't confound Pittsburgh's gunshot detection system

Sophisticated algorithms mean Fourth of July fireworks don’t interfere with ShotSpotter, Pittsburgh’s gunshot detection system.

The system gives police a better way to pursue illegal celebratory gunfire, said Dan Shak, the Public Safety Department’s technology manager.

“We continually analyze incidents within ShotSpotter, looking at certain time periods during those holiday seasons,” he said. “Whether it be New Year’s Eve or Fourth of July, we look to deploy resources to those areas that are known to have illegal gun and firework activity.”

The technology uses acoustics to detect when a gun is fired and then pinpoint the location from which it was fired.

Shak said just because the sensors detect a sound does not mean it becomes an alert that is passed on to police.

The sensors capture the time, location and audio related to sounds it picks up, including the blast that gives gunfire its loud “crack.” That combination of information is processed by machine algorithms in the ShotSpotter system, which determines whether the sound is gunfire, fireworks, a car backfiring or something else.

The algorithm, Shak said, is generally 95% accurate.

Earlier this year, city officials approved expanding the ShotSpotter technology to cover nearly 18 square miles of the city. Previously, the technology covered just a 3-square mile section of Homewood in the Zone 5 police area.

In 2016, the most recent full year for which data was available, there were 479 ShotSpotter activations in July. Of those, 400 did not lead to an officer being dispatched. Every other month that year averaged about 64 notifications, most of which led to the dispatch of an officer.

“The number of events that come in to ShotSpotter versus the number of events that are passed on as alerts are different,” he said. “ShotSpotter will receive notifications of cars backfiring or fireworks, but those are either disqualified by that machine algorithm” or the people monitoring the system.