Payment processor Square is making its credit card readers for mobile devices available at even more retailers in the US, including Walgreens, Staples, and FedEx Office stores. While you’ve always been able to order one of the dongles for free from Square’s website, the company has been trying to grow its retail presence in the past year, selling the readers for $9.95 everywhere from Apple stores to Best Buy and Wal-Mart. Buying the dongle at a retail store gets you a $10 rebate that you can redeem once you sign up for Square's service.

When plugged into your mobile device's headphone jack and combined with an iOS or Android app (no Windows Phone support yet), the readers let you swipe your credit card to pay for purchases, effectively turning your phone or tablet into a point of sale terminal. Recently, Square has been branching out into other areas of the mobile payment space, too, releasing its Square Register iPad app to compete more directly with traditional cash registers. The company says that its readers are now available at 20,000 retailers across the US, but that number drops to zero abroad, while competitor PayPal has been going aggressively after the international market.