Abstract: An expandable apparatus and method configured for inserting into a mammalian stomach and adapted for sensing the activity of the stomach wall. The apparatus comprising: a) an inflatable balloon insert-able into the stomach, when deflated; and b) one or more sensors, mounted to the external surface of the balloon. The inflatable balloon is adapted to attach the one or more sensors to the stomach wall, when the balloon is fully inflated in the stomach; such that the sensors are immovably affixed to the stomach wall, sufficient to sense at least one of mechanical-activity and electric-activity, emanating from the stomach wall.