The Police Department began using gunshot detection technology early last month in two 1.5-square-mile areas to try to better pinpoint the location of gunshots, Superintendent Garry McCarthy disclosed Thursday. The sensors sometimes give officers information before 911 calls are made, he said.

In the past decade, the city twice installed the devices but ultimately removed them because of their high price tags and ineffectiveness. Since then the technology has improved “dramatically,” McCarthy said.

“What we can do with this is overwhelming right now,” McCarthy said at a news conference. “It’s gotten a lot better, and obviously as it’s out there longer, it’s a lot cheaper also.”

The one-year contract for the ShotSpotter system costs about $200,000 — money that will come from drug forfeitures and other property seized by police, authorities said.

via Chicago Tribune.

So it didn’t work before and was too expensive.  Boy, that’s not what we were told last time.

Given the success of the pilot program, in September 2003, Mayor Daley announced that a new phase of PODs would be deployed throughout the City. Subsequently, the number of PODs increased from 30 to 80 by December 2003. Some of the new second generation PODs were also equipped with technology to detect gunfire. Using wireless technology, these units transmitted gunshot alerts, as well as the usual video images, directly to the City’s Emergency Management and Communications Center, thereby providing crucial intelligence on criminal incidents involving guns. Several of the 30 existing PODs were also upgraded with the same technology during that time period.
— CPD Website, dated June 15, 2003

and

Chicago police plan to add 50 new remote-controlled cameras in city … The new cameras will be equipped with gunshot detectors….
— Herald & Review, dated April 7, 2004

and

Chicago police have installed 30 surveillance units in high-crime locales. The system uses four microphones to zero in on firearm discharges.
— USA Today, dated June 6, 2005

The USA Today article ends with:

Adding SENTRI to an existing surveillance camera is not cheap, however. The system costs between $4,000 and $10,000 per unit. In Chicago, money forfeited by criminals is used to pay for both it and the accompanying cameras.

As a result, Police Superintendent Phil Cline told a recent U.S. Conference of Mayors meeting, “the drug dealers are actually paying to surveil themselves.”

I guess everything old is new again.