An anonymous reader quotes a report from The Stack: Researchers at the University of Michigan have created an app that makes any smartphone pressure-sensitive without additional hardware. The app, called ForcePhone, uses ultrasonic tones in the existing microphone and speaker hardware that respond to pressure for additional functionality for touchscreens. The app emits a high-frequency ultrasound tone from the device's existing microphone, which is inaudible to humans but can be picked up by the phone. That tone is calibrated to change depending on the pressure that the user gives on the screen or on the body of the phone. This gives users an additional way to interact with their device through the app alone. The additional functionality provided by ForcePhone can be used in a number of ways. Squeezing the body of the phone could take a user back a page, for example; or increased pressure on the touchscreen could act as a 'right-click' function, showing additional information on the app in use. Kan Shin, Professor at the University of Michigan, said, "You don't need a special screen or built-in sensors to do this. Now this functionality can be realized on any phone." He added, "We've augmented the user interface without requiring any special built-in sensors. ForcePhone increases the vocabulary between the phone and the user."