Abstract: A system and method for detecting the presence of a skimmer in the credit card reader of a kiosk such as a gas pump, ATM or other self-service vending machine which conducts the transaction directly with the consumer without interaction of an attendant or clerk. A light source and a light sensor are located on either side of a card slot on the credit card reader. When the light source is blocked from the light sensor for a predetermined length of time, an alarm is triggered. The alarm may notify an attendant or security to investigate any issues with the credit card reader. The light source is pulsed on and off at a predetermined frequency to differentiate it from ambient light and other light sources.