CHARLOTTE, N.C. -- Stay on patrol while you're at the gas pump. Law enforcement has a warning as thieves are on the prowl when you least expect it.

"It's shocking," said Rene Gonzalez.

Police say stay vigilant after a number of crimes have been committed at gas stations recently.

Authorities say don't let your guard down because police are seeing problems at the pump.

Earlier this week at a gas station near SouthPark Mall, a woman was robbed at gunpoint.

"Always come just pump my gas and the car's always unlocked," said Jonnie Wysong.

Law enforcement is seeing a troubling trend nationwide. They're calling these crooks sliders. They strike when you're pumping gas. If your car is unlocked, they crouch down and go into your vehicle undetected and take what they need.

Police advice patrons at gas stations to lock your doors and roll up your windows.