The smartphone is an extension of the body. We know when we lose it because we feel empty without it.
“Though its precise dimensions may vary with fashion, a smartphone is fundamentally a sandwich of aluminosilicate glass, polycarbonate and aluminum sized to sit comfortably in the adult hand, and to be operated, if need be, with the thumb only. This requirement constrains the device to a fairly narrow range of shapes and sizes; almost every smartphone on the market at present is a blunt slab, a chamfered or rounded rectangle between eleven and fourteen centimeters tall, and some six to seven wide. These compact dimensions permit the device to live comfortably on or close to the body, which means it will only rarely be misplaced or forgotten, and this in turn is key to its ability to function as a proxy for personal identity, presence and location.”