Charge it to my subway card please!

Yesterday, I was waiting for the subway, and noticed a korean girl buying a drink with her subway card at this machine!  

I couldn't believe it!  I had to try it for myself!  Sure enough, I just held my subway key charm up to this little box, chose my drink, and wala, 1 diet coke fell! 

I love the level of technology and resourcefulness in this country!