Retailers experimenting with biometric payments Three or four days a week, Darren Hiers gets lunch at a Sterling convenience store near the car dealership where he works. He grabs a chicken sandwich and a soda and heads to the checkout counter, where a little gadget scans his index finger and instantly deducts the money from his checking account ....... The finger scan used at the shop in Sterling, known as a biometric payment system and made by a Herndon firm, is just starting to be installed at convenience stores and supermarket chains around the country, another step in a revolution...