When government agencies consider acquiring and using surveillance systems, communities and their elected officials must both weigh the benefits against the costs to civil liberties and carefully craft policies and procedures that help to limit the negative effects that surveillance will have on fundamental rights.  For a useful list of considerations, please visit the recommendations page.

The technology is far from perfect – and could raise very serious privacy concerns if not carefully calibrated to detect only gunfire. The Justice Department lauds these devices for picking up over 99 percent of shots fired within their range (a very low false-negative rate). However, these devices have been known to pick up noise from firecrackers and car backfires (a much higher false-positive rate). Some gunshot detectors have even captured and recorded loud conversations. Officials in communities using this technology must adopt policies to ensure that they are only sensitive enough to monitor gun violence and are not used to monitor or record the activities of ordinary people.

In 2011, the chief of the Detroit Police Department lobbied hard to get the cash-strapped city to spend $2.6 million on a gunshot detection system. The chief hoped that the system would cover the high-crime eastern, western, and downtown areas of the city. Proposing to pay for the system with a combination of seized drug money and grants from the Department of Justice, the department insisted that the system was necessary to curb deaths from gun violence, which had risen about 20 percent over the previous year. The city council, however, remained skeptical. First, the deal amounted to a multi-million dollar equipment rental. The city would merely lease, rather than own, the gunshot detectors, a steep investment for a nearly-bankrupt community. Second, as one council member pointed out, the detectors couldn’t respond to gun crime on their own. While the gunshot detection system would reveal violence in real time, the city couldn’t afford enough officers to respond to all of the alerts. With this point in mind, the council postponed the project indefinitely. Detroit’s experience shows that the backbone of crime-fighting is a visible police force that the public trusts. New technology should supplement, not replace, traditional community policing.

Gunshot detectors use many of the same techniques geologists use to monitor and locate seismological activity. Newer models use a combination of acoustic and infrared sensors to spot gunfire.

Originally developed in the mid-1990s, early gunshot detection tools quickly attracted the interest of local police and the Pentagon. In Iraq and Afghanistan, the military used gunshot detectors extensively to locate snipers and insurgents. Today, gunshot detector companies boast that their latest models not only detect gun discharges and relay the location of the incident to police, but also identify the caliber of the gun used and count the number of shooters.  Local authorities must ensure that the equipment is not used to monitor your lawful activities – even if you happen to live in a high-crime neighborhood.

According to the New York Times, more than 70 communities around the country have acquired extensive gunshot detection systems, including large cities like New York, Boston, Minneapolis, and San Francisco. Cities that use ShotSpotter, the most popular system, also subscribe to the company’s monitoring service, which interfaces directly with the city’s police communications center.  The city of Seattle has considered installing ShotSpotter’s detection system.

Gunshot detectors recognize the sound of gunfire and pinpoint its location. A community experiencing a wave of violence may find it useful, but police should not use it to eavesdrop on normal conversations and activities.