External smart microphone for mobile phones

Mobile phones are gaining popularity as sensing platforms. They already come with a set of built-in sensors, such as GPS, accelerometer, microphone and radio, enabling interesting applications. Furthermore, several systems exist where external sensors are interfaced with mobile phones to monitor medical conditions or support environmental sensing, for example. In this paper, we present an external acoustic sensor that interfaces with a mobile phone to support continuous monitoring of sounds in the environment. The on-board electronics samples the microphone, performs signal processing and detection tasks and sends the events of interest to the mobile phone via Bluetooth. The main reasons the built-in microphone is not able to support such an application is the high power usage of continuously sampling and processing the acoustic signal on the phone and the fact that the typical phone is carried in a pocket or bag shielding the microphone from the environment. Our particular motivating application is a mobile phone-based countersniper system which is also presented.