ForcePhone is a novel system for enabling phones to recognize the force applied to their touchscreen and/or body. ForcePhone uses built-in sensors to measure the applied force via a physical property called structure-borne sound propagation. The phone plays an inaudible sound through the phone's speaker. When the phone is free to vibrate, the sound from the speaker easily travels through its body to the phone's microphone. When a force is applied to the phone, vibration is restricted and the sound traveling through the pathway is degraded. ForcePhone estimate the amount of applied force by monitoring the change in sound degradation.