This document describes technologies for interpreting physical contact with a non-touchscreen portion of a computing device's housing (e.g., the computing device's case) as input. For example, a user tapping his/her index finger against the back of a computing device, such as a smartphone or a tablet computing device, can be interpreted as input and can cause an operation to be performed by the computing device, such as turning the page of an electronic book that is being displayed by the computing device.