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.

What is it used for?

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.

How It Works

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.

  • Gunshot detectors are large acoustic sensors. Mounted by the dozen on utility poles and the sides of buildings, they form expansive geographic networks that cover whole neighborhoods.
  • Gunshot detectors sense several unique characteristics of gunshots.  They are set up to recognize the sound of a bullet blast, the “crack” of a projectile moving at supersonic speeds, and a visible muzzle flash. Ideally, the detectors lie dormant until a gun is fired, at which point the system’s microphones and infrared cameras activate.
  • When someone fires a gun, multiple sensors detect the noise and record the precise moment the sound reached the sensor. The volume of the shot and tiny differences in the time it took the sound to reach the sensor establish the distance of the shot from each detector. A computer uses this information to triangulate the location of the shooter. The most advanced models available to large police departments can recognize more than one shooter. Some even identify the caliber of the weapons.
  • In an ideal situation, police respond with more speed and precision than in the past. Whereas eyewitness accounts of a shooting are often fuzzy, gunshot detectors pinpoint the location of a shooting to within a few yards and can tell officers what to expect when they arrive (e.g., if the shooter was moving on foot or in a car).

Civil Liberties Concerns

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.

How Prevalent Is It?

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.

Examples Of Use

Location: Detroit, MI
Gunshot Detectors Not A Viable Solution For High-Crime Detroit

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.

“The right of the people to privacy is recognized and shall not be infringed. The legislature shall implement this section.”

Article 1, Section 22 of the Alaska Constitution.