I have written about IC Cards, such as Suica and Pasmo.
But let’s assume you are planning to go back to Japan and are not sure how much money you have on your IC Card.
Fortunately, there is an app called Suica Reader and if you have a newer android phone like Samsung 7 or so, you can easily find out how much yen you have on your card.
Here is a quick video I made on how to use Suica Reader: