Amazon.com unveiled Amazon Local Register, a $10 credit-card reader and mobile app for brick-and-mortar businesses on Wednesday, expanding its presence in the physical world. The move pits Amazon against a slew of rivals, including startup Square, which popularized a payments dongle that allowed businesses to quickly accept credit and debit cards.

For those who sign up after October, Amazon will take a 2.5 percent cut of each card swipe, still less than Square's 2.75 percent flat transaction rate and PayPal's 2.7 percent.