SIOUX FALLS, S.D. (KELO) -- Over the weekend, Sioux Falls police responded to an unusually high number of stolen cars. From Friday to Monday morning, thieves got away with nearly 40 vehicles. 18-year-old arrested in east Sioux Falls shooting "That's still an ongoing problem we have of people just, for whatever reason, are leaving keys inside their vehicles. The other half of that, or roughly half of that were Kia or Hyundai cars," said police spokesman Sam Clemens. Some vehicles, like Kias and Hyundais, are being stolen even though the keys haven't been left in them. A manufacturing issue has made them an easy target. "And so people figured out a way to exploit that, to be able to, basically it was easy for them to figure out how to steal a car by using that manufacture issue. So I think Kia, Hyundai, I think if you would take the car to the dealership, they would, retroactive, be able to change something like that," said Clemens. Keeping other types of cars from being stolen is even easier. "Not leaving keys in the car is paramount. It doesn't matter if the car is locked. It's easy for somebody to get in," said Clemens. And if you want to warm up your car in the winter, Clemens says that's fine- as long as you keep an eye on it.