Square has gone from giant of the smartphone-enabled mobile payment scene to scrappy underdog now that major players like Google and the ISIS network have started paying attention. It appears like the company is staying in the mix through technological innovation, however, and the latest example of that is the new version of its Card Case app for iOS.

If you're not familiar, Card Case allows you to open a tab (the traditional kind, not the browser kind) with businesses that use Square for checkout and then pay simply by verifying your identity with the clerk. The new update adds to that functionality by taking advantage of a new feature in iOS 5, geo-fencing. At a user's discretion, the app can be set to "Always Auto Open Tab" when you are within 100 meters of a business, which will allow you to pay without even pulling your iPhone out of your pocket. Your tab automatically closes itself when you leave. It's a location-based combination of check-in and, well, checking out.

Square has signed up 20,000 merchants with the Card Case payment system since launching it eight weeks ago and the app has a directory so you can find companies that support the tab system.