And as they try to prevent thefts, they spot some major mistakes by some shoppers that make it easier for thieves.
"This one's got a purse laying in the front seat here," says Sgt. Dan Pashon as he checks cars for any valuable items left inside while the owners are shopping.
It's part of the Puyallup Police Department's effort to prevent car prowls and make drivers more aware of the risk. In some cases, police are leaving notes on car windows to remind drivers not to leave valuables inside while shopping.
There's already been one attempted break-in at a local Best Buy parking lot, and officers hope to prevent more such incidents.
"I think folks get comfortable, and they don't realize while you're inside shopping, there's people outside shopping in the parking lot for themselves," says Sgt. Pashon.
During one Saturday patrol, officers found vehicles with money, purses, mail and GPS devices - all in plain sight.
But a lot of other shoppers are already cautious.
"I think about it all the time you bet. Try to be really cautious - really careful," says shopper Lili Myher.
Another shopper, Judy Boettcher, says, "If I go in and shop and have a lot of stuff ... I'll move my car."
Prowlers are peeking through windows of parked cars in the daytime and at night. They use tools to break in or smash windows.
"They're not worried about the cost of repairing your window - they just want what's inside and it doesn't take long to get it," says Sgt. Pashon.
And police say you should never leave your garage door opener on your car. It's one of the most common items people forget when they leave their vehicles, but if thieves get your registration and garage door opener your home can become an easy target.
"It's a shame - that's the times we're in right now. It's common sense - unfortunately you hear it too much," says another shopper.
In addition to stepping up patrols in parking lots, police are also setting up DUI checkpoints. That's happening now through New Year's Eve.