TAMPALate one night in April, Hillsborough sheriff's Lt. Dennis Fogarty was about to get into his patrol cruiser when he heard four distant — but distinct — popping sounds from his perch off E Fletcher Avenue.He paused, then looked at his watch.It took 32 seconds for the alert to sound on his in-car laptop.Four gunshots. The computer pinpointed them at N 19th Street, five blocks south.When Fogarty arrived at the scene, deputies were swarming the apartment complex. A red Dodge Durango sport utility vehicle sat in the parking lot, its back window shattered. On the ground nearby were four shell casings.No one called 911. No witnesses could be found."If I had to go looking for where those shots came from, there is absolutely no way I would have found it," Fogarty said. "We would have never known."But this time they did find the scene of the shooting, because ShotSpotter told them.• • •The April 30 shooting was one of hundreds of shootings that have been detected in Hillsborough County using ShotSpotter, a gunshot triangulation system that the Sheriff's Office purchased last year.It uses a network of sensors — essentially, very sensitive microphones — to detect when and where gunshots are fired in public.Between Jan. 1 and June 24, the Sheriff's Office has recorded 239 incidents of gunfire.Multiple gunshots accounted for 108 of those incidents, or 45 percent. There were 97 single gunshots, or 40 percent. Together, that's 205 confirmed shootings, or 86 percent of the incidents detected by Shot Spotter. The rest, 34 incidents, were classified as "possible gunfire."Altogether, the totals amount to two to three shootings a day. Some were homicides."Our understanding of where gunfire is occurring has changed dramatically," said Capt. David Fleet, who helped implement the technology. "A lot more illegal gunfire happens than we were aware of."Hillsborough County's three-year contract with ShotSpotter was finalized in October. In November, the company installed 80 sensors on light poles, on rooftops, and in other spots high off the ground in two of the county's heaviest concentrations of gun crime.Those are the neighborhoods west of the University of South Florida, known among deputies as "the box;" and the neighborhoods around Nuccio Park, including the area deputies call "the fishbowl," because of the aquatic theme to its street names.ShotSpotter is one of several tools deputies can use to identify when and where crimes take place. It is used in concert with the agency's 38 "Eye on Crime" surveillance cameras, stationed on top of light poles throughout the same areas.The gunshot detection system uses Time Difference Of Arrival (TDOA) positioning, a mathematical technique used as far back as World War I to locate enemy artillery fire. It works by measuring the slight differences in the time it takes for a sound to travel to multiple locations. Those differences can then be used to calculate the approximate location from where the sound came.When three or more sensors detect possible gunshots, the noises are recorded and transmitted to ShotSpotter headquarters in Newark, Calif. There, the sounds are quickly analyzed. An animated visualization of the sounds depicts gunshots as distinct spikes.Confirmed gunshots prompt an alert, which is sent to officers working that area. A map, pinpointing the approximate location when the shots were fired, accompanies the alert.The Hillsborough County Sheriff's Office is one of about 90 American police agencies that use ShotSpotter, according to SST Inc., the company that produced the system. It is the only agency in the Tampa Bay region to use the technology.• • •But the implications of detecting and pinpointing gunshots go beyond law enforcement.An academic analysis of the technology from the Brookings Institution, a Washington, D.C., think tank, concluded that ShotSpotter could provide important data for researchers to help them make a more accurate measurement of gun violence in the United States.That's because people aren't consistently reporting gunshots to police. The Brookings study found that just 12 percent of gunfire incidents in Washington, D.C., and Oakland, Calif., resulted in a 911 call.The company reports that cities which have used its system have seen the number of gunfire incidents decline by as much as 50 percent over several years.But that claim has been questioned. A report on ShotSpotter earlier this year from the Center for Investigative Reporting found little evidence that it reduces crime. The report examined ShotSpotter calls in San Francisco over a 2½-year period. In that time, the report said, 3,000 ShotSpotter alerts produced just two arrests.Other cities that have used the technology have also been criticized by civil liberties groups concerned that the system erodes privacy and expands public surveillance.It's also expensive. The Hillsborough County Sheriff's Office paid more than $800,000 for the equipment, software, and subscription to ShotSpotter. The money came from a crime prevention trust fund.Jennifer Doleac, a University of Virginia economics and public policy professor who co-authored the Brookings study, said more research needs to be done to better assess ShotSpotter as a crime-fighting tool."The jury is still out about what effects ShotSpotter has on public safety, arrest rates, and local residents' relationship with the police," Doleac said. "There haven't been any good evaluations looking at those outcomes, partly because local officials haven't pushed for them and partly because the cities that pay for ShotSpotter typically don't own the data it produces."Doleac added that it is crucial that local governments begin insisting on ownership of ShotSpotter data, which the company thus far has insisted is proprietary and not part of the public sphere."If taxpayer dollars pay for data collection," Doleac said, "the public should own those data."So far, Hillsborough sheriff's officials say, it has been worth the investment.Case in point: a shooting on Memorial Day. The ShotSpotter alert came in at 6:07 a.m. on May 30. It pinpointed the gunshot to E 136th Avenue and N 23rd Street. Deputies arrived within two minutes. They found a trail of blood, according to the Sheriff's Office, leading to the back of a nearby Target store, where a man lay wounded.The man was hospitalized. An investigation into the shooting is continuing."Potentially, it saved his life," Fleet said. "If not, it got us there a lot quicker."Contact Dan Sullivan at [email protected] or (813) 226-3386. Follow @TimesDan.