According to the statistics, people upgrade smartphones at every two years, which means tremendous number of phones will be left unused. In this paper, we propose a method to use Android-based smartphones as wireless sensors for environmental monitoring. Although the idea of using smartphones as a wireless sensor sounds naive, the previous approaches were un-practical because of its limited battery life. In this paper, we exploit the Linux kernel boot mode on Android devices to extend the battery life drastically. Unlike normal mode, power consumption in the kernel mode is minimum but still it is possible to access to all the sensors in principle. In this paper, we measure the power consumption of Nexus5 while booting, running and shutting down Android OS / Linux kernel and estimate the battery life assuming a duty cycle. The results show that utilizing the Linux kernel can extend the battery life up to 10.9 times when the sensing interval is 3 minutes.

Pedestrians have difficulty noticing hybrid vehicles (HVs) and electrical vehicles (EVs) quietly approaching from behind. We propose a vehicle detection scheme using a smartphone carried by a pedestrian. A notification of a vehicle approaching can be delivered to wearable devices such as Google Glass. We exploit the high-frequency switching noise generated by the motor unit in HVs and EVs. Although people are less sensitive to these high-frequency ranges, these sounds are prominent even on a busy street, and it is possible for a smartphone to detect these signals. The ambient sound captured at 48 kHz is converted to a feature vector in the frequency domain. A J48 classifier implemented on a smartphone can determine whether an EV or HV is approaching. We have collected a large amount of vehicle data at various locations. The false-positive and false-negative rates of our detection scheme are 1.2% and 4.95%, respectively. The first alarm was detected as early as 11.6 s before the vehicle approached the observer. The scheme can also determine the vehicle speed and vehicle type.