An electronic device with a front side including a touch-sensitive display, a back side that does not include a display, and sensor(s) to detect contact intensities on the front and back side displays, on the touch-sensitive display, a user interface including objects. While displaying the user interface, the device detects an input on a side of the electronic device. In response, for a front side input with intensity that meets first criteria, the device performs a first operation corresponding to a first object; for front side input with intensity that meets second criteria, the device performs a second operation corresponding to the first object; for back side input with intensity that meets third criteria, the device performs a third operation that changes the user interface; and for back side input with intensity that does not meet the third criteria, the device maintains display of the user interface.