Suzane Loi has been perched behind the cash register at The Coffee Mill in Oakland, Calif., for 27 years, watching the daily thrum of Grand Avenue through the cafe’s huge windows.

Lately, she has been unnerved by the view.

Thieves have broken into cars at the gas station across the street as their owners stood in disbelief at the pumps, she said. Several times a week, masked burglars have smashed the windows of vehicles parked near her shop.

The Coffee Mill itself has been robbed three times in the last six months, so frequently that her annual insurance premiums have doubled to $12,000.

“When I park my car, I leave my windows open this much,” Ms. Loi said with a note of resignation, holding her hands apart several inches, wide enough to let someone reach into her vehicle without shattering glass.

The surge in crime — in such brazen waves that some community groups have publicly suggested that the National Guard was needed — has shaken even the most loyal residents of Oakland, a city of 420,000 that has long seen itself as California’s scrappy answer to San Francisco.