You won’t hear it with the human ear, but the next time you are in a big chain store, Shopkick may be calling out your name!

According to a recent article at Forbes.com, Shopkick is a location-based customer loyalty app like Foursquare or Gowalla, but with an important difference:

…it doesn’t use the phone’s GPS. Instead, Shopkick uses a different technology. It plugs in a small box inside each participating store. The box emits a high frequency sound that humans can’t hear. When the Shopkick app is opened, it recognizes the sound so that it knows that the person is actually in the store.

The bottom line is engagement. Remember a few posts ago we were talking about the difference between TV ads that are just on, shooting dumbly out into the atmosphere, versus web ads that tease you and make you click? If you click the web ad, you are already interested in the product. That’s engagement, and the same principle applies with Shopkick. You physically go into the store, you turn on the app, and you wait for the deals to come to you. And Shopkick claims a success rate of 45% that, if it’s true, is a really high number!

For now, because it requires hardware, Shopkick is mainly in large chains like Target, Best Buy, Macy’s, Disney and so on. Foursquare uses existing satellite tracking, and it is popular with smaller independent stores. But of course, they are looking into copying Shopkick’s success. Hopefully the winner will be YOU.

So have you used Shopkick? What do you think?