PALMER PARK, Md. — It’s a winter tradition: Warnings from police departments about keeping your car safe from thieves. But departments all across the region keep repeating it, because people keep making the same mistakes that lead to cars, wallets and other items getting taken.

“This is a 100 percent preventable crime,” said Prince George’s County Police Cpl. Harry Bond, talking about what police call “warm-up” thefts.

“That’s when individuals go out and warm up their vehicles in the morning … and opportunists come by, they see the vehicles being warmed up unattended, keys in the ignition, and they jump in the car and drive off.”

Bond said sometimes people go out looking to steal a car, combing neighborhood streets to find a running car that no one is watching.

“It only takes a matter of seconds for your vehicle to be gone,” Bond said. “Especially with the keys in the ignition.”

Other times, stealing a car can be a spur-of-the-moment decision.

“In some instances, the individual is walking to a destination” on the kind of cold day no one wants to be outside in. They may not have started out looking to steal a car “but they see one unattended, and it’s a warm vehicle, and now you’ve provided warm transportation to their destination.”

Before the month of January had even ended police had documented 37 such car thefts. In dozens of more cases, police say wallets, purses, electronics, and other items of value, including a passport, were taken out of cars that had been left unlocked.

“If you are warming up your vehicle, stay with your vehicle so that you can keep your vehicle,” Bond said. “Would you leave a winning lottery ticket in a driveway so that someone could come by and take that winning lottery ticket? Would you leave your purse or your wallet on the counter of a retail store and just walk away? I don’t believe that you would, so please don’t leave your keys in the ignition so that someone can take your vehicle in the morning.”