Residents are being warned to keep their eyes open the next time they fill up at the gas pump.

Someone has been installing scanning devices known as "skimmers" inside credit card readers at gas stations across the county. Capable of stealing credit or debit card information, including pin numbers, and used to make fraudulent purchases, victims are encouraged to notify authorities and not attempt to remove the devices themselves.

The San Diego County Sheriff's Department has partnered with local and federal agencies to investigate these crimes. Several arrests have already been made. The investigation is ongoing.

Here are things you can do to protect yourself:

• Use the gas pump closest to the building. Most "skimmers" are installed far away from the view of the gas station clerk.

• Look closely at the gas pump and make sure the seal by the lock has not been broken. If the seal is broken, alert the clerk immediately.

• Don't use a card reader or keypad that is loose or raised above the surface of the gas pump panel.

• Use cash and pay inside.

• When possible, use a credit card at the pump because it offers better fraud protection.

• Always check your bank statements for any signs of fraud.

• If you are a victim, call your local law enforcement agency.