This week the San Diego Police Department announced it has deployed a new system to detect and pinpoint gunshots in four of the City’s most dangerous neighborhoods.

The new audio receiver system uses microphones installed at least 30 feet above the ground to monitor sounds in a neighborhood. When a sound is detected, the system triangulates the sound to determine the location where it happened. If the system suspects it was gunfire, police would be dispatched.

San Diego Police announced the system has been deployed in the communities of Valencia Park, Skyline, O’Farrell and Lincoln Park.  The system gives police information on the location and time of the shooting, the number of rounds, and how many different locations the shots originated from. SDPD did not release information as to the locations or number of individual microphones used by the system.

The police department did test the system this week by firing 36 gunshots. No report of the results of the audio detections was released.

The system, called ShotSpotter, is leased from a private company, Newark, California-based SST, Inc. and will cost $245,000 for a one-year program. The system has been deployed in 90 cities worldwide, including several large U.S. cities, including New York, Milwaukee, and Miami.

The manufacturer released a report called the National Gunfire Index, highlighting the successes of their system. The report concludes that 36 of 46 cities they tracked in 2015 experienced a decrease in incidents of gunfire. And in those cities with reduced gunfire, 19 of them saw decreases of  20 percent or more.

Still, critics argue that this system, and others like it, focus policing on minority communities, which can lead to over policing in communities already targeted by police, and often do not result in significant cases of crimes.

In Florida, for example, a review of a ShotSpotter program by the Miami Herald found that, after one year of operation, only one in four alerts of gunfire resulted in a prosecutable case.

Privacy advocates have also raised issues with the fact that the system records all sounds for 72 hours before overriding the recordings. Additionally, local critics have complained that police departments and city officials did not hold public meetings or invite community input in deploying the system or determining the areas where it would be deployed.

In October 2015, General Electric agreed to begin embedding ShotSpotter sensors into its next-generation streetlights as part of its Intelligent Environments for Cities platform, which is creates a networked ecosystem of smart streetlights to provide traffic, weather, and audio service for cities. The deployment of ShotSpotter may increase dramatically throughout the country.

SDPD will evaluate the results of the system’s alerts after the first year to determine its effectiveness.