In 2010, the Square device communicated with the Square app through a phone's audio jack.
The Square Reader was the first product released by Square. It is used to accept credit card payments by connecting to a mobile device's audio jack. Square's original reader consisted of a simple read head directly wired to a 3.5 mm audio jack, strong encryption on its devices, including SSL and PGP. Its cryptographic keys are at least 2,048 bits in length. Neither card numbers, nor magnetic stripe data, nor security codes are stored on Square client devices. Square follows the guidelines issued by OWASP.
accept chip cards and contactless cards. This new reader supports chip-and-signature and contactless transactions, and the standard Square Reader is also provided in order to support traditional magnetic stripe card transactions.
Accepting Apple Pay and other contactless payments, in addition to EMV chip cards.