Square enables users to accept card payments on Android devices. Square reads magnetic stripe data through the microphone port using a free reader and sends receipts via email or SMS. Square has been featured in the Android Market and at Google I/O.

Bob and Eric, the programmers behind Square, will demonstrate how magnetic stripe decoding works. They’ll describe Square's unique approach to Intent-based APIs used in the point-of-sale API. They’ll share tips for taming the activity stack and building device-independent user interfaces.

Finally, they’ll give a sneak peak into their upcoming open source Android library Retrofit. Retrofit provides utilities for dependency injection (using Google Guice), simple and fast persistence, REST communication and dialog management.