Loop is here, and it’s kind of magical - the phone case sends wireless signals to a credit card swiper simply by waving the smartphone like a magic wand. This sorcery works by mimicking the magnetic swipe signals cards send to credit card readers, and it purportedly works without any changes to current POS (point of sale) systems.
How it works:
The MST technology generates changing magnetic fields over a short period of time. This is accomplished by putting alternating current through an inductive loop, which can then be received by the magnetic read head of the credit card reader. This signal received emulates the same magnetic field change over time as when a magstripe card is swiped across the same read head. Loop works within 4 inches from the read head; the field dissipates rapidly beyond that point, and only exists during a transmission initiated by the user (as opposed to NFC).
The case comes with a card reader you use to upload your card to the Loop wallet app, where it stays stored until you do the Loop wave. Unfortunately, the case is only compatible with iPhone 5 and 5s, while the fob (plugs into your headphone jack and works the same) is compatible with iPhone 4. Loop promises Android compatibility for the fob in Q1 2014, but no word from them yet about the case. Android users should consider Coin, another card alternative that puts all of your cards into one.