LOVELAND, Ohio (AP) — Authorities in southwest Ohio are warning motorists about a string of credit-card “skimmer” devices discovered on gas pumps in recent weeks.

Hamilton County Auditor Dusty Rhodes told WLWT-TV authorities are investigating after two credit card skimmers were found at gas stations in Loveland.

A skimmer is a device placed inside the credit card reader that captures credit and debit card information as the card is being swiped for payment. It slightly resembles a thumb drive and can’t be detected from the outside of a pump.

Rhodes said similar devices were found at gas pumps in West Chester last month. Warren and Butler county officials said they’ve found the devices in previous months.

Police have said the individuals who install the skimmers will drive a large box truck or moving truck to block cameras pointing at the pump, making it hard to track down those responsible.

“There’s got to be something that they can do — some kind of alarms they can put on the machines —to recognize that someone’s doing something that shouldn’t be done,” said Loveland resident Rachel Moore.

A Butler County gas station is putting tamper-proof stickers over the pump panels. Officials are recommending that credit card users pay inside the gas station.