How does a touch screen that doesn't use a stylus work?

heat sensitivity?

pressure?

i guess the same way, just pressure, it measures the X and Y axis, just not as accurate as stylus ofcourse in terms of total accuracy, then again, the might take the center of the complete touched surface, not sure though

capacitance-the screen is comprised of layers including a conductive layer, that can register tiny changes in voltage; your fingers have a very low voltage in them, so this is registered in a matrix that is in the capacitance layer of the touchscreen.