Generally, if you go through the gate holding a ICOCA card and another IC card over the checker, one atop the other, the gate won't let you pass but will issue an error beep; however, with some of the IC cards such as your IC driver's license, you can pass the gate without a problem.
他のICカードと2枚重ねにしてかざすとエラー音が鳴って改札を通れなくなるが、IC運転免許証など、ICOCAと重ねても問題なく利用できるICカードもある。