The Chicago Police Department plans to put more gunfire-location sensors in two high-crime districts to combat the extraordinary violence gripping those parts of the city.

ShotSpotter Flex sensors now cover about 3 square miles of the city in the Englewood District on the South Side and the Harrison District on the West Side.

The city plans to increase the coverage to more than 13 1/2 square miles at a first-year cost of about $940,000. The sensors are leased from SST Inc. in California, which provides ShotSpotter technology to police departments across the country.

The city will pay for the increased sensors with money from asset forfeitures.

“Those two districts will be completely covered,” Chicago Police Deputy Chief Jonathan Lewin said. “We think this will improve first responder safety and awareness.”

The department also plans to boost the number of blue-light surveillance cameras in those same two districts by 25 percent, Lewin said.

Chief police spokesman Anthony Guglielmi said the additional technology is a “force multiplier” that will better allow the department to put cops where they’re needed right away.

He said the department hopes the extra sensors will also help improve community relations in those two police districts because officers will respond more quickly to shootings there.

The department first installed ShotSpotter technology in 2003 but gave up on the sensors because they generated numerous false hits, Lewin said.

In 2012, after the technology had been greatly improved, then-police Supt. Garry McCarthy put the sensors in the Englewood and Harrison Districts, Lewin said. The sensors also have picked up shootings in small parts of two adjacent districts.

From 2014 to March of this year, the sensors have alerted police to 1,600 gunshots in the Englewood and Harrison Districts combined, Lewin said. On average, the ShotSpotter sensors notified the department of gunshots five minutes faster than calls to 911, he said.

Many times, there is no call to 911, Lewin said.

SST Inc. guarantees the sensors can locate a gunshot within a 25-meter radius, Lewin said.

When sensors triangulate the location of a shot, the company’s analysts in California evaluate the sound to confirm it came from a gun. Then they notify the police.

Up to now, officers learned of ShotSpotter hits over the police radio.

But the department plans to integrate officers’ mobile computer terminals with the ShotSpotter system so they will get an alert and see the location of the shots on a map along with live-streamed images from any nearby blue-light surveillance cameras.

Those updates will occur this year, Lewin said.

He said the police department will improve its analysis of ShotSpotter data. The patrol division can use the information to see how often gunshot notifications have led to arrests and where clusters of shootings are happening. Detectives can process bullet casings found at shooting scenes to make connections to other cases.

A police supervisor who works in one of the districts where the sensors are deployed said his officers have arrested fleeing suspects after a ShotSpotter identified gunfire at particular addresses.

“We hear it a lot on the radio — ‘I have ShotSpotter showing six shots fired at such and such location,’ ” said the supervisor, who asked that he not be named. “Sure, this has led to bad guys with guns before.”

Still, the supervisor said he was unsure whether expanding the use of the sensors will significantly curtail shootings.

“These guys just don’t care,” he said. “It’s bad out there.”

In addition to the expanded technology, Mayor Rahm Emanuel is promising to hire more cops to turn the bloody tide in Chicago.

If the pace of killings continues here, the city could reach levels of murder not recorded since the ’90s when there were more than 900 homicides annually. The number of murders in the city surpassed 500 after Labor Day, more than in Los Angeles and New York combined. There have been more murders this year than all of last year.