PressMic: Multi-Level Press Input on Commodity Devices Using Built-in Microphones

Abstract

We present PressMic, a passive acoustic method that enables multi-level press input on commodity devices using built-in microphones. PressMic introduces a notched annulus around the microphone vent, forming a compact press-sensitive acoustic interface. Upon finger contact, the device enclosure and the annular boundary create a local acoustic configuration near the vent. A light press produces a detectable resonance from the front cavity, whereas a hard press blocks the vent and suppresses acoustic coupling. PressMic uses a two-stage, event-driven signal pipeline that first detects press events and then classifies them as light or hard. We validate the mechanism with controlled cavity-variation experiments and evaluate the system on a commodity smartphone under ambient sound levels ranging from 25 to 85 dB. Under these conditions, the first-stage detector achieves 96.1% accuracy, the second-stage classifier 95.9%, and the complete pipeline 94.2% accuracy with a Macro-F1 score of 0.932 for three-state recognition. These results demonstrate that passive acoustic modulation using built-in microphones—especially noise-canceling or array types—enables multi-level press input with only a low-profile, cleanable structure around the vent, without active sensing or extra sensors.