The Android Smartphone as an Inexpensive Sentry Ground Sensor
Abstract
A key challenge of sentry and monitoring duties is detection of approaching people in areas of little human traffic. We are exploring
smartphones as easily available, easily portable, and less expensive alternatives to traditional military sensors for this task, where the
sensors are already integrated into the package. We developed an application program for the Android smartphone that uses its
sensors to detect people passing nearby; it takes their pictures for subsequent transmission to a central monitoring station. We
experimented with the microphone, light sensor, vibration sensor, proximity sensor, orientation sensor, and magnetic sensor of the
Android. We got best results with the microphone (looking for footsteps) and light sensor (looking for abrupt changes in light), and
sometimes good results with the vibration sensor. We ran a variety of tests with subjects walking at various distances from the phone
under different environmental conditions to measure limits on acceptable detection. We got best results by combining average
loudness over a 200 millisecond period with a brightness threshold adjusted to the background brightness, and we set our phones to
trigger pictures no more than twice a second. Subjects needed to be within ten feet of the phone for reliable triggering, and some
surfaces gave poorer results. We primarily tested using the Motorola Atrix 4G (Android 2.3.4) and HTC Evo 4G (Android 2.3.3) and
found only a few differences in performance running the same program, which we attribute to differences in the hardware. We also
tested two older Android phones that had problems with crashing when running our program. Our results provide good guidance for
when and where to use this approach to inexpensive sensing.
Description
Proc. SPIE Conf. on Unattended Ground, Sea, and Air Sensor Technologies and Applications XIV, Baltimore, MD, April 2012
Rights
This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.Collections
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