A retired NYPD detective was one of the people who jumped into action when a man pulled a gun out at a North Babylon gym.

Joseph Koch and two other gym members at LA Fitness wrestled the gunman down Tuesday.

He credits his police training and nine years of experience with the NYPD for spotting the man acting suspicious.

“It didn’t add up…the sunglasses, the full-face mask and looking around very aggressively,” Koch says.

After he alerted the manager, they confronted the 18-year-old when someone screamed, he had a gun.

Koch says he made sure held the man’s hand and gun so he could direct it away from other people.

The retired NYPD detective says that the gunman told him he was going to shoot him.

Then the gun went off.

Police arrived and arrested the gunman they identified as Noah Hayes.

“He did fire one shot going toward the vending machines, but luckily I was directing the firearm to a safe location,” Koch says.

He was also a hero in 2013 when he was off duty leaving a party in Queens.

A boy ran out of a house screaming and Koch saw a man beating a woman.

During a struggle, Koch’s gun went off and injured his hand. He was later recognized by former President Barack Obama for his bravery.

Koch, a father of four girls, says helping people is in his nature even if it means risking his own life.

“My oldest is probably three or four younger than the gentleman who was going to get shot,” Koch says. “It’s always in my heart to help out when I can.”