Vital signs (e.g., the breathing rate) monitoring has become increasingly important because it can offer useful clues to medical conditions such as sleep disorders or anomalies. There is a compelling need for technologies that enable contact-free, easily deployable, and long-term vital signs monitoring for healthcare. In this chapter, we focus on acoustic-based vital signs monitoring for which related acoustic-based sensing techniques with smartphones are introduced. Then, we present the SonarBeat system to exploit a phase-based active sonar for monitoring breathing rates with smartphones. We design and implement the SonarBeat system, with components including signal generation, data extraction, received signal preprocessing, and breathing-rate estimation, with Android smartphones. Our experimental results validate the superior performance of SonarBeat in various indoor environment settings.
