An activated ShotSpotter monitor in Huntington Station early Saturday morning led to the arrest of a man who police charged with illegal possession of a handgun, authorities said.

Officers responded to the signal that went off at 4:51 a.m. on Lenox Road and found a group of people congregating after a party had broken up, said Det. Sgt. James Scimone, with the Suffolk County Police second squad.

Among the group was Cristian Rodriguez, 24, who was carrying an unloaded 9-mm handgun, Scimone said. Rodriguez, who lives on Lenox Road, was charged with fourth-degree criminal possession of a weapon, police said in a news release. He is being held overnight until Sunday when he is scheduled to be arraigned at First District Court in Central Islip on Saturday.

Attorney information for Rodriguez was not immediately available. Attempts to reach family members were unsuccessful Saturday afternoon.

Detectives scoured the location and found a shell casing, but no spent bullets were recovered, Scimone said. While the shell casing “appears” to match a 9-mm handgun, Scimone said the squad is awaiting ballistics testing to confirm where it came from.

“At that point, it would still be further investigated. We would have to prove that he fired a shot,” Scimone said about upgrading any charges against Rodriguez.

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The suspect has not been cooperative with police, Scimone said, and the events leading up to the ShotSpotter activation are still unclear.

ShotSpotter, designed to pinpoint the sources and direction of gunfire in order to speed police responses in areas where residents are afraid to speak out, has been used in several Suffolk communities, including North Amityville, Huntington Station, Wyandanch, Brentwood and North Bellport. It has received criticism for its usefulness since its inception in the county in 2011.

Other than a gun shot, fireworks, “or a loud retort of something like that,” could also activate the ShotSpotters, Scimone said.