The shooting happened in the Upper Dimond neighborhood, where residents in a five-block area hired a company called Security Code 3 last fall and touted the guards' presence with signs on their lawns.
Just before noon, one of the firm's uniformed guards interrupted a burglary at a home on Harding Way, said police Capt. Rick Orozco. The guard spotted at least two people trying to make off with a flat-screen television and a telescope, police said.
The guard chased one of the suspected burglars in his Toyota Corolla - marked with the words "Private Patrol" and with an amber light bar on the roof - before getting out of the vehicle and chasing the man, Orozco said.
The pursuit ended in the driveway of Caria Tomczykowska's home on the 4000 block of Waterhouse Road, where the suspect, described as being about 18 years old, turned toward the guard with a screwdriver, police said.
The guard fired a single shot, wounding the man in the leg, police said.
Residents said they had opted for private patrols because of a spike in burglaries in their neighborhood from 2011 to 2012. They pay $475 a year per household.
Tomczykowska said the guard who shot the suspect was "just a remarkable man" and a "hero for the neighborhood today." Police have not identified him.
Tomczykowska said of the shot suspect, "I'm sorry that this young man got himself into the situation that he did, but I hope that the leg wound will slow him down for a good time to come."
Petro Petreas said he lives next to the house on Harding Way that was burglarized. He called the guard service "an extra layer of protection that can be helpful, and it seems like today they responded and did the job the way they're supposed to."
The shot suspect was being treated at Highland Hospital and was expected to survive. His name has not been released. A second man fled the scene in a Mercedes-Benz SUV and abandoned it in nearby Dimond Park, police said.
The guard who shot the suspect is part of the neighborhood's regular patrol, said Richard McDiarmid, regional manager for Security Code 3.
"Situations like this, you can't foresee," McDiarmid said. "Security business is basically 'observe and report.' Unfortunately, sometimes things escalate that are beyond our control, and self-defense comes into play."
He added that the guards' goal "is to be seen. We're a deterrent. Hopefully the people that are committing crimes, they see that there's security in the area and they go to a different area, quite frankly."
Many Oakland residents have hired private guards to conduct patrols in their neighborhoods.
"I wasn't sure how I felt about it at first, just because it seems almost like a privileged thing to have," said Marianne Vlahos, who lives on Waterhouse Road near the site of Thursday's shooting. "But yeah, it makes me feel more comfortable."