Active Elements in Phone/Tablet Cases
Soon you will be able to use your phone, and a sensor case, to check your blood glucose level, for diabetics. You can expect that whatever cases appear that are really useful, and those that sell well, are likely to come out for either iPhone or Android; but they won't necessarily come out for every model of Android since there are so many.
We are inching toward a world that has medical tricorders, except that they will be more common than anticipated; they can potentially be part of every phone!