HAYWARD (CBS SF) — Shoppers in in Hayward were being warned to pay extra attention at the checkout counter after Hayward police discovered a credit card skimmer that is easy for thieves to install, and very hard to detect.

The devices look identical to credit card machines. They fit loosely and can quickly and easily slip on and off.

Officers found one such skimming device at a Hayward store after employees noticed the credit card reader was not working.

Police warn shoppers to be on the lookout for phony credit card readers and report any suspicious devices to the police immediately.