Amazon has announced the expansion of its palm payment technology, Amazon One, in Whole Foods stores across the US. The technology allows customers to pay for items by scanning their palm once linked to a credit card. The system is already in use at more than 200 Whole Foods stores and Amazon plans to introduce it at the remaining 300 by the end of the year. The company says that users’ palm signatures are unique and encrypted, and that no data is stored on the devices upon which the scanning takes place.